Multi-spectral laser array and optical system

ABSTRACT

An organic vertical cavity laser light producing device ( 10 ) comprises a substrate ( 20 ). A plurality of laser emitters ( 200 ) emits laser light in a direction orthogonal to the substrate. Each laser emitter within the plurality of laser emitters has a first lateral mode structure in a first axis orthogonal to the laser light direction and has a second lateral mode structure in a second axis orthogonal to both the laser light direction and the first axis. Each laser emitter comprises a first mirror provided on a top surface of the substrate ( 20 ) and is reflective to light over a predetermined range of wavelengths. An organic active region ( 40 ) produces laser light ( 350 ). A second mirror is provided above the organic active region and is reflective to light over a predetermined range of wavelengths. A pumping means excites the plurality of laser emitters.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 10/304,078, filedNov. 25, 2002, entitled ORGANIC VERTICAL CAVITY LASER AND IMAGINGSYSTEM, by Kurtz et al.

FIELD OF THE INVENTION

The present invention relates to electronic display and printing systemsgenerally, and more particularly to electronic display and printingsystems that employ organic laser light sources.

BACKGROUND OF THE INVENTION

Laser based electronic imaging systems have been developed for use bothin projection display, and even more extensively, for printingapplications. In particular, laser projection display systems have beendeveloped with several basic architectures, which include vectorscanning, raster scanning, one-dimensional (1-D) scanning, andtwo-dimensional (2-D) area imaging systems. The development of laserprojection systems, which are typically intended to be multi-color, havebeen generally limited by the minimal availability of useful visiblewavelength lasers. On the other hand, laser based printing systems havebeen extensively developed using all of these same architectures, withthe possible exception of vector scanning. As a result, many of thelaser beam shaping and laser beam modulation techniques applicable tolaser projection have been previously developed in great detail andvariation by the efforts directed to laser printing. Notably, however,most of the laser printing systems described in the prior art aremonochrome, and utilize infrared lasers, rather than the multiplevisible spectrum lasers desired for laser projection.

In a typical laser printer, radiation from a laser is shaped, and imagedonto a film plane to produce the desired spot size. The spot, called apixel, forms the smallest image element of the image. The laserradiation is modulated to create the correct density of each spot, pixelby pixel. The laser spot is scanned in the line direction, and the mediais moved in the page scan direction to create a two-dimensional image.In a printer system with a continuous wave (CW) gas or solid statelaser, an external modulator, such as an acousto-optical device, isoften used to input the image data into the optical beam. Whereas, insystems with semi-conductor diode lasers, the laser radiation istypically modulated directly by varying the current input to the laser.For printers using high sensitivity media such as a silver halide film,high printing throughput is obtained by scanning the laser beam in theline direction with a polygonal mirror or a galvanometer. These printersare called “flying spot” printers.

By comparison, when the print media has a low optical sensitivity (suchas most thermal media), the typical laser printer employs high powerlaser sources and slow line and page scan speeds to meet the highexposure requirements. One way to achieve this type of scan is toconfigure the printer like a “lathe,” where the page scan is obtained byrotating a drum which holds the film, and line scan, by translating thelaser in a direction parallel to the axis of rotation of the drum. Toachieve this high optical power throughput, in a small package, with arelatively low cost, the technology has adapted to provide multiplewriting spots directed to the target plane.

Multi-spot printers have been configured in systems using a single laseras the light source, where the light illuminates a linear spatial lightmodulator array, which is in turn imaged to the target plane. Exemplarysystems are described in several prior art patents, including U.S. Pat.No. 4,389,659 by Sprague, U.S. Pat. No. 4,591,260 by Yip, and U.S. Pat.No. 4,960,320 by Tanuira. However, the high power single beam lasers aretypically too large and expensive to use in many printing applications.Moreover, such systems are sensitive to the potential failure of thelaser source.

In another approach, a monolithic array of laser sources is imageddirectly onto a light sensitive media to produce multiple spots. Thepower to each element of the laser array is individually modulated toobtain pixel densities. Such a system, as described by U.S. Pat. No.4,804,975, potentially has a low cost and high light efficiency. On theother hand, this type of system is susceptible to emitter failure, andthe consequent introduction of a pattern error. It can also be difficultto properly modulate the diodes, due both to the high current inputsneeded by the diodes and the sensitivity to thermal and electricalcrosstalk effects between laser emitters.

As a hybrid approach, linear diode laser arrays are used as lightsources without direct addressing, and the laser light from themultitude of emitters is subsequently combined to flood illuminate alinear spatial light modulator array. In many such systems, the lasingemitters provide single mode Gaussian light emission in the cross arraydirection, and spatially multi-mode emission in the array direction. Atypical emitter might be ˜100 μm in length in the array direction, andonly 3 μm wide in the cross array direction. The addressed pixels of themodulator array break up the light into image elements, and each pixelof the modulator is subsequently imaged onto the media plane to form thedesired array of printing spots. Printing systems employing thisapproach are described by prior art patents U.S. Pat. No. 4,786,918 byThornton et al., U.S. Pat. No. 5,517,359 by Gelbart, and U.S. Pat. No.5,521,748 by Sarraf. A variety of linear spatial light modulators areappropriate for use in such systems, including the “TIR” modulator ofU.S. Pat. No. 4,281,904 by Sprague, the grating light valve (GLV)modulator of U.S. Pat. No. 5,311,360 by Bloom et al., the electro-opticgrating modulator of U.S. Pat. No. 6,084,626 by Ramanujan et al., andthe conformal grating modulator of U.S. Pat. No. 6,307,663 by Kowarz.Certainly numerous other modulator array technologies have beendeveloped, including most prominently the digital mirror device (DMD)and liquid crystal displays (LCDs), but these devices are less optimalas linear array modulators which experience the high incident powerlevels needed in many printing and display applications.

In such systems, it is important that the illumination provided to themodulator plane be as uniform as possible. To begin with, if the emittedlight is spatially and temporally coherent from one emitter to the next,the overlapped illumination at the modulator can suffer variation frominterference fringes. Even with laser array consisting of long 1-Dmultimode emitters, laser filamentation, residual coherence, andnon-uniform gain profiles can cause significant macro- andmicro-non-uniformities in the array direction light emission profiles,which can result in the modulator illumination being significantlynon-uniform. These issues have been addressed by a variety of methods.

As an example, U.S. Pat. No. 4,786,918 provides a laser diode array inwhich alternating single mode laser emitters are offset in one of tworows, so that the emitters are uncoupled and mutually incoherent. Theemitted light subsequently overlaps in the far field, without anyassistance from light homogenizing optics, to provide a substantiallyGaussian light profile without interference.

In contrast, prior art U.S. Pat. Nos. 5,517,359 and 5,521,748 bothutilize linear laser diode array consisting of broad area emitters.These high power laser arrays used in these systems typically emit 20-30Watts of near infrared light, at wavelengths in the 810-950 nm range,with emission bandwidths of 3-4 nm. In both of these systems, the laseremitters are imaged directly, in an overlapping fashion, with theassistance of a lenslet array, onto the modulator array at a highmagnification. As the array direction light emission profile for each ofthese emitters suffers a light fall off at the ends of the emitters, thesystem of U.S. Pat. No. 5,517,359 provides a mirror system to partiallycompensate for these problems, by substantially removing themacro-nonuniformities, but at the cost of some reduced brightness due tothe increased angular spread of the illumination to the modulator. Themethod of U.S. Pat. No. 5,517,359 also only works well when the lightprofile across the emitting elements already has large areas that aresubstantially uniform.

A variety of systems have been disclosed for improving the illuminationuniformity provided to the spatial light modulator array from the laserarray. In particular, U.S. Pat. No. 5,923,475 by Kurtz et al. describessystems where a fly's eye integrator is used to homogenize the arraydirection illumination incident to the modulator array. Similarly, U.S.Pat. No. 6,137,631 by Moulin utilizes an integrating bar to homogenizethe light.

As these laser diode arrays also typically suffer from “laser smile”,which is a cross array deviation of the emitter location fromco-linearity (typical total deviation is 10 μm or less), cross arrayoptics have been developed to correct for this problem. A variety ofsmile correction methods are described in prior art patents U.S. Pat.No. 5,854,651 by Kessler et al., U.S. Pat. No. 5,861,992 by Gelbart, andU.S. Pat. No. 6,166,759 by Blanding. Laser diode array bars have alsobeen stacked in the cross array direction, with the goal of increasingthe incident light available to the target plane. Exemplary laser beamshaping optics designed for stacked laser arrays are described in priorart patents U.S. Pat. No. 6,215,598 by Hwu and U.S. Pat. No. 6,240,116by Lang et al.

Numerous color laser printers, with color lasers or infrared lasers andfalse color media, have been developed. In general, the most thoroughlydeveloped architecture for color laser printing utilizes co-alignedbeams in a flying spot printer. Exemplary prior art patents include U.S.Pat. No. 4,728,965 to Kessler et al. and U.S. Pat. No. 4,982,206, alsoto Kessler et al.

However, the visible color laser systems used both in display andprinting applications have under utilized this very effectivearchitecture of having a laser diode array flood illuminate a spatiallight modulator array, with or without intervening light uniformizingoptics. The system described in U.S. Pat. No. 5,982,553 by Bloom et al.utilizes solid state lasers (red, green, and blue) to illuminate aspatial light modulator array, which is turn imaged and scanned across ascreen. As with the comparable laser printing systems, U.S. Pat. No.5,982,553 system relies on a single laser source (for each color), andis thus sensitive to the failure of that laser source.

In the prior art patents U.S. Pat. No. 5,614,961 by Gibeau et al. andU.S. Pat. No. 5,990,983 by Hargis et al., color laser arrays aredirectly modulated and scanned across the screen. Thus, these systems donot utilize a system architecture which flood illuminates a spatiallight modulator array, and thus the systems lack laser redundancy, andthey too are sensitive to laser emitter failure. Additionally, the colorlaser arrays described by U.S. Pat. Nos. 5,614,961 and 5,990,983 arecostly and difficult to fabricate. Because the laser arrays rely oninorganic semiconductor or solid-state laser media which do not emitlight directly in the blue (440-470 nm) and green (520-550 nm) regionsof the spectrum, nonlinear optics are required to frequency double thelight emission to the desired wavelengths. Reliable lasers based on thenitride system that emit sufficient power directly in the blue and greenspectral regions do not appear to be available in the near future. Forthe present, the nonlinear optics increase the cost and complexity ofthe laser arrays, and also reduce the efficiency of the laser system.Furthermore, the requirement to directly modulate the laser arrays inU.S. Pat. Nos. 5,614,961 and 5,990,983 necessitates the inclusion of anexternal modulating element to each emitter in the laser arrays to avoidchirp in semiconductor laser systems or limits due to the long upperstate lifetime in solid-state laser systems.

Therefore, it can be seen that a laser projection display system usingthe optical system architecture combining a laser diode array with aflood illuminated spatial light modulator array would be advantaged.Moreover, it can be seen that improved, robust, low cost, color laserdiode arrays would be advantaged over the existing color laser arrays,and would in turn further advantage this same optical systemarchitecture.

One new laser technology that could be particularly advantaged forproviding visible wavelength laser arrays, which could be useful bothfor projection and display, is the organic vertical cavity laser.

Vertical cavity surface emitting lasers (VCSELs) based on inorganicsemiconductors (e.g. AlGaAs) are more commonly known than are the newer,organically based lasers. Inorganic VCSELs have been developed since themid-80's (“Circular Buried Heterostructure (CBH) GaAlAs/GaAs SurfaceEmitting Lasers” by K. Kinoshita et al., IEEE J. Quant. Electron. QE-23,pp. 882-888 (1987)), and they have reached the point where AlGaAs-basedVCSELs emitting at 850 nm are manufactured by a number of companies andhave lifetimes beyond 100 years. With the success of these near-infraredlasers, attention in recent years has turned to using inorganic materialsystems to produce VCSELs emitting in the visible wavelength range, butdespite significant efforts worldwide, much work remains to createviable inorganic laser diodes spanning the visible spectrum.

In an effort to produce visible wavelength VCSELs it would beadvantageous to abandon inorganic-based systems and focus onorganic-based laser systems, since organic-based gain materials may havea number of advantages over inorganic-based gain materials in thevisible spectrum. For example, typical organic-based gain materials havethe properties of low unpumped scattering/absorption losses and highquantum efficiencies. In comparison to inorganic laser systems, organiclasers should be relatively inexpensive to manufacture, can be made toemit over the entire visible range, can be scaled to arbitrary size and,most importantly, are able to emit multiple wavelengths (such as red,green, and blue) from a single chip.

Given this potential, interest in making organic-based solid-statelasers is increasing. In the efforts to date, the laser gain materialhas been either polymeric or small molecule, with these materialsutilized in a variety of resonant cavity structures. The exemplarycavity structures used have included micro-cavity structures (U.S. Pat.No. 6,160,828 by Kozlov et al.), waveguide structures, ringmicro-lasers, and distributed feedback structures (U.S. Pat. No.5,881,083 by Diaz-Garcia et al.). Notably, these new devices have allused a laser pump source to excite the organic laser cavities.Electrical pumping is generally preferred, as the laser cavities aremore compact and easier to modulate.

A main barrier to achieving electrically-pumped organic lasers is thesmall carrier mobility of the organic material, which is typically onthe order of 10⁻⁵ cm²/(V-s). This low carrier mobility results in anumber of problems. Devices with low carrier mobilities are typicallyrestricted to using thin layers in order to avoid large voltage dropsand ohmic heating. These thin layers result in the lasing modepenetrating into the lossy cathode and anode, which causes a largeincrease in the lasing threshold (“Study of lasing action based onFörster energy transfer in optically pumped organic semiconductor thinfilms” by V. G. Kozlov et al., J. Appl. Phys. 84, pp. 4096-4106 (1998)).Since electron-hole recombination in organic materials is governed byLangevin recombination (whose rate scales as the carrier mobility), lowcarrier mobilities result in orders of magnitude more charge carriersthan singlet excitons. One consequence of this is that charge-induced(polaron) absorption can become a significant loss mechanism. Assuminglaser devices have a 5% internal quantum efficiency, while using thelowest reported lasing threshold to date of ˜100 W/cm² (“Lightamplification in organic thin films using cascade energy transfer” by M.Berggren et al., Nature 389, pp. 466-469 (1997)), and ignoring the abovementioned loss mechanisms, would put a lower limit on theelectrically-pumped lasing threshold of only 1000 A/cm². Including theseloss mechanisms would place the lasing threshold well above 1000 A/cm²,which to date is the highest reported current density, which can besupported by organic devices (“High Peak Brightness PolymerLight-Emitting Diodes” by N. Tessler, Adv. Mater. 19, pp. 64-69 (1998)).

One way to avoid some of the problems affecting electrical pumping oforganic laser devices is to use crystalline organic material instead ofamorphous organic material as the lasing media. For example, an organiclaser, comprising a thick layer single crystal tetracene gain materialand a Fabry-Perot resonator, has demonstrated room temperature laserthreshold current densities of approximately 1500 A/cm².

However, it would be preferable to fabricate organic-based lasers withamorphous layers instead of crystalline layers (either inorganic ororganic materials), as the manufacturing costs are significantlyreduced. Furthermore, amorphous organic lasers can more readily befabricated over large areas, as compared to producing large regions ofsingle crystalline material. Additionally, because of their amorphousnature, organic-based lasers can be grown on a wide variety ofsubstrates; thus, materials such as glass, flexible plastics, and Si arepossible supports for these devices. In combination, the amorphousorganic laser has the potential to be scalable to arbitrary size(resulting in greater output powers) and arbitrary shape.

Optical pumping of amorphous organic lasers provides the significantadvantage that the lasing structure is no longer impacted by theproblems experienced by electrical pumping. The organic lasers can bepumped not only by exterior laser sources, but also incoherent lightsources, such as light emitting diodes (LEDs) and lamps. For example,the combinations of using an organic DFB laser with inorganic LEDs(“Semiconducting polymer distributed feedback lasers” by M. D. McGeheeet al. Appl. Phys. Lett. 72, pp. 1536-1538 (1998)) or organic waveguidelasers with organic LEDs (U.S. Pat. No. 5,881,089 by Berggren et al.)have been described. Optical pumping of organic laser systems is enabledby the fact that scattering and absorption losses (˜0.5 cm⁻¹) at thelasing wavelength are greatly reduced, especially when one employs ahost-dopant combination as the active media. Even taking advantage ofthese small losses, the smallest reported optically-pumped threshold fororganic lasers to date is 100 W/cm², in a device using a waveguide laserdesign (“Light amplification in organic thin films using cascade energytransfer” by M. Berggren et al., Nature 389, pp. 466-469 (1997)). Sinceoff-the-shelf inorganic LEDs can only provide up to ˜20 W/cm² of powerdensity, a different device architecture is required to achieve opticalpumping with incoherent sources, particularly with LEDs. In order tolower the lasing threshold additionally, it is necessary to choose alaser structure that minimizes the gain volume; and a VCSEL-basedmicrocavity laser satisfies this criterion. Using VCSEL-based organiclaser cavities should enable optically-pumped power density thresholdsbelow 5 W/cm². As a result practical organic laser devices can be drivenby optically pumping then with a variety of readily available,incoherent light sources, such as LEDs.

There are a few disadvantages to organic-based gain media, but withcareful laser system design these can be overcome. Organic materials cansuffer from low optical and thermal damage thresholds. Devices will havea limited pump power density in order to preclude irreversible damage tothe device. Organic materials additionally are sensitive to a variety ofenvironmental factors like oxygen and water vapor; efforts to reducesensitivity to these variables typically result in increased devicelifetime.

In general, the field of organic lasers has not been fully developed.Moreover, the favorable laser architecture of amorphous organicmaterials, vertical micro-cavity structures, and optical pumping witheither coherent or incoherent light sources, has likewise not been fullydeveloped. In particular, the extension of the optically pumped organicvertical cavity laser into configurations favorable for various systemsapplications has not occurred. As organic lasers, can be fabricated byhigh-vacuum thermal evaporation methods, using masks and photo-resistsfor patterning, a wide variety of laser structures, including laserarray structures can be created. It may also be possible to fabricateorganic lasers in part by utilizing printing methods (as is done withorganic LEDs), such as ink jet or laser thermal deposition. As a result,the organic laser structures can be optimized in new and unique ways tomatch the specific intended applications, such as printing and display.

SUMMARY OF THE INVENTION

An organic vertical cavity laser light producing device comprises asubstrate. A plurality of laser emitters emits laser light in adirection orthogonal to the substrate. Each laser emitter within theplurality of laser emitters has a first lateral mode structure in afirst axis orthogonal to the laser light direction and has a secondlateral mode structure in a second axis orthogonal to both the laserlight direction and the first axis. Each laser emitter comprises a firstmirror provided on a top surface of the substrate and is reflective tolight over a predetermined range of wavelengths. An organic activeregion produces laser light. A second mirror is provided above theorganic active region and is reflective to light over a predeterminedrange of wavelengths. A pumping means excites the plurality of laseremitters.

The invention and its objects and advantages will become more apparentin the detailed description of the preferred embodiment presented below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the structure of a vertical cavityorganic laser.

FIG. 2 is a cross-sectional view of the structure of a vertical cavityorganic laser with improved efficiency of operation.

FIG. 3 is a cross-sectional view of the structure of a vertical cavityorganic laser with phase locking across an array of laser emitters.

FIG. 4 a depicts a perspective view of the organic vertical cavity laserarray of the present invention.

FIG. 4 b depicts an expanded frontal view of a portion of the organicvertical cavity laser emitters within a laser array of the presentinvention.

FIGS. 4 c, 4 d and 4 e depict expanded frontal views of alternateembodiments of a portions of the organic vertical cavity laser emitterswithin an organic vertical cavity laser array of the present invention.

FIG. 5 depicts an imaging system utilizing an organic vertical cavitylaser array of the present invention, wherein the laser array is used incombination with a linear spatial light modulator array.

FIGS. 6 a-6 c are graphs with curves depicting the spatial and angularcharacteristics of the light that could be emitted by the laser emittersof the organic laser array of the present invention.

FIGS. 7 a-7 i depict basic modulation optical systems employing theorganic vertical cavity laser array utilized in combination with spatiallight modulator arrays, with different architectures for illuminatingthe organic vertical cavity laser array.

FIG. 8 a depicts an alternate configuration for a modulation opticalsystem employing an organic vertical cavity laser array utilized incombination with an illumination modulator to provide color sequentialoperation.

FIG. 8 b depicts an alternate configuration for a modulation opticalsystem employing multiple organic vertical cavity laser arrays utilizedin combination with a single spatial light modulator array.

FIG. 8 c depicts an imaging system employing multiple organic verticalcavity laser arrays utilized in combination with multiple spatial lightmodulator arrays.

FIG. 8 d depicts an alternate configuration for an imaging systememploying a multi-color organic vertical cavity laser array incombination with a tri-linear spatial light modulator array.

FIG. 9 a depicts a complete imaging system wherein the vertical cavityorganic laser array is used in combination with a spatial lightmodulator array and other optics and mechanics, in order to scan animage across a target plane.

FIG. 9 b depicts an alternate complete imaging system wherein thevertical cavity organic laser array is used in combination with aspatial light modulator array and other optics and mechanics, in orderto scan an image across a target plane.

DETAILED DESCRIPTION OF THE INVENTION

A schematic of a vertical cavity organic laser structure 10 is shown inFIG. 1. The substrate 20 can either be light transmissive or opaque,depending on the intended direction of optical pumping and laseremission. Light transmissive substrates 20 may be transparent glass,plastic, or other transparent materials such as sapphire. Alternatively,opaque substrates including, but not limited to, semiconductor material(e.g. silicon) or ceramic material may be used in the case where bothoptical pumping and emission occur through the same surface. On thesubstrate is deposited a bottom dielectric stack 30 followed by anorganic active region 40. A top dielectric stack 50 is then deposited.The organic laser film structure 35 comprises the combination of thebottom dielectric stack 30, the organic active region 40, and the topdielectric stack 50. A pump light source 65 provides a pump beam 60 thatoptically pumps the vertical cavity organic laser structure 10. Thesource of the pump beam 60 may be incoherent, such as emission from alight emitting diode (LED). Alternatively, the pump beam may originatefrom a coherent laser source. FIG. 1 shows laser emission 70 from thetop dielectric stack 50. Alternatively, the laser structure could beoptically pumped through the top dielectric stack 50 with the laseremission through the substrate 20 by proper design of the dielectricstack reflectivities. In the case of an opaque substrate, such assilicon, both optical pumping and laser emission occur through the topdielectric stack 50.

The preferred material for the organic active region 40 is asmall-molecular weight organic host-dopant combination that is typicallyorganically grown/deposited by high-vacuum thermal evaporation. Thesehost-dopant combinations are advantageous since they result in verysmall un-pumped scattering/absorption losses for the gain media. It ispreferred that the organic molecules be of small-molecular weight, sincevacuum-deposited materials can be deposited more uniformly thanspin-coated polymeric materials. It is also preferred that the hostmaterials used in the present invention are selected such that they havesufficient absorption of the pump beam 60 and are able to transfer alarge percentage of their excitation energy to a dopant material viaForster energy transfer. Those skilled in the art are familiar with theconcept of Forster energy transfer, which involves a radiation-lesstransfer of energy between the host and dopant molecules. An example ofa useful host-dopant combination for red-emitting lasers is aluminumtris(8-hydroxyquinoline) (Alq) as the host and[4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran](DCJTB) as the dopant (at a volume fraction of 1%). Other host-dopantcombinations can be used for other wavelength emissions. For example, inthe green a useful combination is Alq as the host and[10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-[l]Benzopyrano[6,7,8-ij]quinolizin-11-one](C545T) as the dopant (at a volume fraction of 0.5%). Other organic gainregion materials can be polymeric substances, e.g.,polyphenylenevinylene derivatives, dialkoxy-polyphenylenevinylenes,poly-para-phenylene derivatives, and polyfluorene derivatives, as taughtby Wolk et al. in commonly assigned U.S. Pat. No. 6,194,119.

The bottom and top dielectric stacks 30 and 50, respectively, arepreferably deposited by conventional electron-beam deposition and cancomprise alternating high index and low index dielectric materials, suchas, TiO₂ and SiO₂, respectively. Other materials, such as Ta₂O₅ for thehigh index layers, could be used. The bottom dielectric stack 30 isdeposited at a temperature of approximately 240° C. During the topdielectric stack 50 deposition process, the temperature is maintained ataround 70° C. to avoid melting the organic active materials. In analternative embodiment of the present invention, the top dielectricstack is replaced by the deposition of a reflective metal mirror layer.Typical metals are silver or aluminum, which have reflectivities inexcess of 90%. In this alternative embodiment, both the pump beam 60 andthe laser emission 70 would proceed through the substrate 20. Both thebottom dielectric stack 30 and the top dielectric stack 50 arereflective to laser light over a predetermined range of wavelengths, inaccordance with the desired emission wavelength of the vertical cavityorganic laser structure 10.

The use of a vertical microcavity with very high finesse allows a lasingtransition at a very low threshold (below 0.1 W/cm² power density). Thislow threshold enables incoherent optical sources to be used for thepumping instead of the focused output of laser diodes, which isconventionally used in other laser systems. An example of a pump sourceis a UV LED, or an array of UV LEDs, e.g. from Cree (specifically, theXBRIGHT® 900 UltraViolet Power Chip ®LEDs). These sources emit lightcentered near 405 nm wavelength and are known to produce power densitieson the order of 20 W/cm² in chip form. Thus, even taking into accountlimitations in utilization efficiency due to device packaging and theextended angular emission profile of the LEDs, the LED brightness issufficient to pump the laser cavity at a level many times above thelasing threshold.

The efficiency of the laser is improved further using an active regiondesign as depicted in FIG. 2 for the vertical cavity organic laserstructure 80. The organic active region 40 includes one or more periodicgain regions 100 and organic spacer layers 110 disposed on either sideof the periodic gain regions and arranged so that the periodic gainregions are aligned with the anti-nodes 103 of the device's standingwave electromagnetic field. This is illustrated in FIG. 2 where thelaser's standing electromagnetic field pattern 120 in the organic activeregion 40 is schematically drawn. Since stimulated emission is highestat the anti-nodes and negligible at the nodes 105 of the electromagneticfield, it is inherently advantageous to form the organic active region40 as shown in FIG. 2. The organic spacer layers 110 do not undergostimulated or spontaneous emission and largely do not absorb either thelaser emission 70 or the pump beam 60 wavelengths. An example of anorganic spacer layer 110 is the organic material1,1-Bis-(4-bis(4-methyl-phenyl)-amino-phenyl)-cyclohexane (TAPC). TAPCworks well as the spacer material since it largely does not absorbeither the laser output or the pump beam energy and, in addition, itsrefractive index is slightly lower than that of most organic hostmaterials. This refractive index difference is useful since it helps inmaximizing the overlap between the electromagnetic field antinodes andthe periodic gain region(s) 100. As will be discussed below withreference to the present invention, employing periodic gain region(s)instead of a bulk gain region results in higher power conversionefficiencies and a significant reduction of the unwanted spontaneousemission. The placement of the gain region(s) is determined by using thestandard matrix method of optics (“Design of Fabry-PerotSurface-Emitting Lasers with a Periodic Gain Structure” by Corzine etal. IEEE J. Quant. Electr. 25, pp. 1513-1524 (1989)). To get goodresults, the thicknesses of the periodic gain region(s) 100 need to beat or below 50 nm in order to avoid unwanted spontaneous emission.

The laser can be increased in area while maintaining a degree of spatialcoherence by utilizing the phase-locked organic laser array 190 asdepicted in FIG. 3. In order to form a two-dimensional phase-lockedlaser array 190, lasing emitters 200 separated by inter-emitter regions210 need to be defined on the surface of the VCSEL. Laser emitters arecreated by weakly confining the laser light to emitter regions by eithersmall amounts of built-in index or gain guiding, or by modulating thereflectance of at least one of the mirrors. In the preferred embodimentthe reflectance modulation is affected by patterning and forming anetched region 220 in the bottom dielectric stack 30, using standardphotolithographic and etching techniques, thus forming a two-dimensionalarray of circular pillars on the surface of the bottom dielectric stack30. The remainder of the organic laser microcavity structure isdeposited upon the patterned bottom dielectric stack 30 as describedabove.

The dimensions of the laser emitters are critical for determining thelateral modes supported by the laser emitters. For the case of anindex-guided structures, the number of lateral modes supported isdictated by well-known rules governing optical waveguides (reference:“Theory of Dielectric Waveguides” by H. Kogelnik, Chapter 2 of“Integrated Optics”, Ed. by T. Tamir, Springer-Verlag, 1979, pp. 13-81).For gain-guided structures, the number of lateral modes supported isdictated by the degree of overlap between the supported cavity modes andthe gain profile. For reflectance-modulated structures, the number oflateral modes supported is determined by the dimensions of the mirrorstructure, related to the diffraction loss experienced by a given mode(reference: “Resonant modes in a maser interferometer”; Bell Sys. Tech.J, Vol. 40, pages 453-458, March 1961, by A. Fox and T. Li). Dependingon the guiding structure, a critical dimension exists, below which onlya single transverse mode is supported, and above which a plurality oftransverse modes are supported. These principles apply to laser systemsin general, and are not specific to an organic laser structure.

To obtain phase locking, intensity and phase information must beexchanged amongst the lasing emitters 200. To accomplish this, theinter-emitter spacing, edge to edge, should be in the range of 0.25 to 4μm. Phase-locked array operation also occurs for larger inter-emitterspacings; however, it leads to inefficient usage of the optical-pumpingenergy. Generally, for inter-emitter spacings that have emitter edge toemitter edge distances greater than ˜10 nm coherent coupling will beprovided. The etch depth is preferred to be from 200 to 1000 nm deep toform etched region 220. By etching just beyond an odd number of layersinto the bottom dielectric stack 30, it is possible to affect asignificant shift of the longitudinal mode wavelength in the etchedregion away from the peak of the gain media. Hence, lasing action isprevented and spontaneous emission is significantly reduced in theinter-emitter regions 210. The end result of the formation of etchedregion 220 is that the laser emission is weakly confined to the laseremitters 200, no lasing originates from the inter-emitter regions 210,and coherent phase-locked laser light is emitted by the phase-lockedorganic laser array 190.

One other advantage of the organic VCSEL structures is that they can beeasily fabricated into arrays of individually-addressable elements. Insuch arrays, each element would be incoherent with neighboring elementsand pumped by a separate pump source (e.g. LED or group of LEDs). Thearrays could either be one-dimensional (linear) or two-dimensional(area) depending on the requirements of the application. The elements inthe array can also comprise multiple host-donor combinations and/ormultiple cavity designs such that a number of wavelengths could beproduced by a single array.

The organic gain materials of the present invention exhibit extremelylarge gain bandwidths compared with conventional laser materials. Forexample, Alq doped with the dopant DCM has been reported to have a gainbandwidth exceeding 100 nm (see S. Reichel et al, Very compact tunablesolid-state laser utilizing a thin-film organic semiconductor, OpticsLetters Vol. 26, No. 9, pp. 593-595 (2001)). Therefore, the possibilityexists of producing lasers with a wide range of wavelengths using thesame host-dopant combination. Within an organic laser array of VCSELelements having the same host-dopant combination, the laser wavelengthcan be varied between laser emitters by, for example, controllablyvarying the thickness of the active region. Because the longitudinallaser modes have wavelengths that are proportional to the cavity length,varying the active region thickness produces a laser wavelength thatvaries across the elements.

The specific organic vertical cavity laser array 300 provided by thepresent invention is depicted in FIG. 4 a, and in greater detail in FIG.4 b. In the preferred embodiment of the present invention, each of theindividual laser emitters 330 of this laser array have a linearconfiguration, with multimode lasing behavior in the long axis (X) ofthe emitter, and single mode Gaussian lasing behavior in the short axis(Y) of the emitter. The laser emitters are arranged to form a monolithicorganic laser array, such that representative row 330 comprises multipleemitters 330 a, 330 b, 330 c, . . . 330 k, and row 330 extends along theX axis, such that the long dimension of the emitters is in the same axisas the long dimension of the row. The organic laser array 300 can alsocomprise multiple parallel rows of laser emitters, such as the rows 330,332, 334, . . . 342, that are depicted in FIG. 4 a. The general purposeand value of the organic laser array 300 can be understood byconsidering FIG. 5, where an imaging system 400 includes a modulationoptical system 410 that encompasses an organic laser array (300), aswell as a linear spatial light modulator array 460, and variousintermediate beam shaping optics. As the difficulty of the design andimplementation of imaging system 400 is significantly determined by theoperational and structural characteristics of the laser light source,improvements in the laser sources can have significant impact. Theorganic laser array 300 of the present invention provides opportunitiesboth to improve the design and operation of imaging system 400, and toprovide new capabilities and features for that system.

In particular, the imaging system 400 of FIG. 5 is quite similar to thelaser thermal printing system described in U.S. Pat. No. 5,923,475 byKurtz et al. In that system, the equivalent laser array to the organiclaser array 300 is an array of infrared (1R) laser emitters nominallyoperating at ˜810 nm, where the emitters may be 100-150 μm in length inthe X direction, and <1 μm in height in the Y direction. Due to powerdensity issues in semiconductor laser arrays (particularly high powerarrays), the laser emitters are typically spaced on a pitch much largerthan the emitter length (500-650 μm for example). In the infrared laserthermal system, light in the array direction (X) is used to floodilluminate a modulator array (460), with a fly's eye integrator (440)providing light homogenization, and with the laser emitters (330)conjugate to the spatial light modulator. Array field lens 436 can beused to make the illumination telecentric to the modulator array 460, oralternately, to image the fly's eye integrator into the pupil of theimaging lens 470. Unlike the laser array depicted in FIG. 5, theinfrared laser array shown in U.S. Pat. No. 5,923,475 is a semiconductordevice providing only a single row of laser emitters. Generallyspeaking, it is very difficult to create a multiple row semi-conductorlaser array (U.S. Pat. No. 4,803,691 by Scifres et al. provides anexample of one), and multiple row arrays are generally only provided bystacking laser arrays, or by coupling multiple lasers to a multi-rowoptical fiber array. Such multi-row structures are costly, mechanicallycomplicated, and may be significantly limited in terms of the minimumpitch possible between adjacent rows.

Semiconductor laser arrays also typically suffer from a manufacturingproblem known as “smile”, where the emitter positions along the row varyfrom co-linearity in the Y direction. As smile error impacts the crossarray beam size at the modulator array, with a possible impact on lightefficiency or modulation performance, a combination of optical andmechanical methods have been developed to correct for this problem,including those described in U.S. Pat. No. 5,854,651 by Kessler et al.and U.S. Pat. No. 6,166,759 by Blanding.

As compared to the semiconductor laser arrays, including the infraredlaser arrays used in thermal printing, the organic laser array 300offers several potential advantages to an imaging system 400. To beginwith, organic lasers can provide visible wavelength laser light overmuch of the visible spectrum, whereas, by comparison, semiconductorlasers have been limited to particular red and blue lasing wavelengths.Moreover, as organic lasers can be fabricated readily, using patternprinting techniques, it is relatively easy to create multi-row arrays,with the laser emitters within each of the rows placed with highaccuracy (negligible smile error). Additionally, the lasing wavelengthscan be readily varied across the organic laser array in a deliberatemanner. Organic laser arrays have these and other significant advantagesover semiconductor laser arrays, which in turn provide both advantagesand new capabilities to an imaging system 400 constructed with theseorganic laser arrays.

This can be better understood by considering the organic laser array 300depicted in FIGS. 4 a and 4 b in greater detail. Organic laser array 300comprises a multitude of rows (330 through 342) of laser emitters (suchas 330 a through 330 k) fabricated on a single monolithic substrate 310.As shown in detail in FIG. 4 b, which depicts a portion of an organiclaser array 300, the generalized laser emitters 328 have a length (L), awidth (w), a pitch (p) between emitters within a row, where the length(L) is less than the pitch (p), thereby leaving a gap 325. Likewise,there is a pitch (p2) between rows of laser emitters. In FIG. 4 b, thelaser emitters 328 are referred to as “generalized” so that the organiclaser array 300 can be described in broadest terms, as compared to thedescription of the organic laser array 300 and the laser emitters 330 a,330 b, 332 a, etc., accompanying the discussion of FIG. 4 a throughoutthis patent, for which many design variations are considered.

Preferably, the organic laser array 300 is optically pumped, using backillumination from an external light source. In FIG. 4 a, this is shownsimply with light source 360 providing illumination light 365 ofwavelength(s) λi, and organic laser array 300 emitting laser light 350of wavelength λc. The illumination light 365 is transmitted through thesubstrate 310, which is preferably optically transparent, to providepump light to the organic laser emitters populating the organic laserarray 300. For example, light source 360 may be an incoherent lightsource such as an LED, which emits light λi from ˜380 to ˜420 nm, whilethe organic laser emitters can be generally be constructed to emit lightacross most of the visible spectrum, with a given laser emitterproviding output light at a set lasing wavelength λc with a limitedbandwidth (for example at 532 nm with a+/−0.5 nm bandwidth). As will bediscussed in great detail later, the illumination light 365 can beprepared and optimized by a variety of different illumination opticalsystems.

Most simply, the organic laser array 300 could be constructed so thateach emitter nominally emits light at the same wavelength (again such as532 nm). However, as organic laser emitters can be constructed withconsiderable deliberate variation in lasing wavelength, and as thesevariations can be created in a deliberate manner across the laser array,the organic laser array 300 can be constructed to provide a great rangeof lasing wavelengths from a single monolithic substrate 310. Forexample, organic laser array 300 could be fabricated with an emitterpattern such that the first row of laser emitters 330 comprised laseremitters 330 a-330 k that operated at one given nominal wavelength(λc1), while the second row of laser emitters 332 could comprise laseremitters 332 a-332 k that operated at a second given nominal wavelength(λc2). For example, λc1 might be 532 nm, while λc2 might be 620 nm.Thus, organic laser array 300 could be constructed with each row havinga different nominal lasing wavelength, or with groups of rows of laseremitters having the same or nearly the same nominal lasing wavelength,while other groups of rows of laser emitters on the same array 300 couldhave different wavelengths (from each other and from the first group).Likewise, the organic laser array 300 could be constructed so that thelasing wavelength is deliberately varied amongst the laser emitterswithin a given row. The ease with which the lasing wavelength can bedeliberately varied across the organic laser array 300 is veryadvantageous in contrast to the difficulties encountered in attemptingsimilar variations with semi-conductor or solid-state laser arrays. Asan example, U.S. Pat. No. 5,384,797 by Welch et al. describes a complexmonolithic multi-wavelength laser diode array that includes an array oflaser oscillators, coupled to an array of Bragg reflector gratings andthen coupled both to a laser amplifier array and a frequency doublingwaveguide array, to thereby provide a multi-wavelength laser array withless flexibility in layout and wavelength than is provided by theorganic laser array 300. As will become apparent, certain configurationsand combinations for varying the lasing wavelengths across an organiclaser array 300 are particularly advantageous for the imaging systemsconsidered in the present application.

It should be understood that the organic laser array 300 depicted inFIG. 4 a is representative only, and that a device with 7 rows ofemitters, each possessing just 11 laser emitters, is useful forexplaining the concepts of this invention. For example, an actual devicecould be fabricated with laser emitters periodically spaced in an arrayover several cm² area. As a further example, if the rows are then spacedat a 10 μm period (p2), with each row having 150 μm wide (L) emittersspaced on a 250 μm pitch (p), a 3 cm by 3 cm organic laser array 300would have ˜360,000 laser emitters. At present, optically pumped organiclaser arrays have demonstrated rather modest conversion efficiencies. Inparticular, patterned arrays have demonstrated ˜10-20% conversionefficiency of the pump light (UV) into output laser light, whileexhibiting a low damage threshold, relative to the power density of thepump light (<1 W/cm²). This means that an organic laser array with a 10cm² area can accept ˜10 Watts of input UV light from the pump source, toprovide ˜100 to 200 mw of visible wavelength output laser light from thelaser array. Although these output power levels are modest, the abilityto scale the output power with device area and also to select thevisible spectra lasing wavelengths has significant potential for certainapplications in image printing and projection.

As shown in FIGS. 4 a and 4 b, the organic laser array 300 of thepresent invention preferentially comprises laser emitters 328 that arelong (in X) and narrow (in Y) in construction. More preferentially, thegeneralized laser emitters 328 are multimode laser sources in X, andsingle mode laser sources in Y. To accomplish this, the generalizedlaser emitters 328 have a length (L) in X sufficiently large to supporta plurality of lateral laser modes and a width (w) in Y sufficientlysmall to support only a single lateral laser mode. An exemplary laseremitter might have a “height” (w) in Y of ˜2-5 microns, and a 100 μm“length” in X. The single mode emitted light is preferentially nominallyGaussian (with the M² parameter defining the beam quality), with a halfangle beam width β, as illustrated in FIG. 6 a, where curve “a”represents both the spatial (ω) and angular beam (β) profiles. When thegeneralized laser emitters 328 are single mode laser sources in the Ydirection, the height (w) corresponds to twice the Gaussian beam waistradius (ω). The multi-mode emitted light has a half angle beam width α,and angular and spatial beam profiles that are not Gaussian, but broad,and preferentially uniform until the edges are reached. Using generalconvention, the angular widths α and β both are defined to extend to the1/e² point (˜13% power level) of the angular intensity profile (whetherthe profile is Gaussian in shape, or not). As shown in FIG. 6 b, thespatial beam profile is ideally uniform (see curve “b”) over the emitterlength L, but a somewhat rounded profile (curve “c”) can be acceptable.A noisy spatial beam profile (curve “d”), which can for example becaused by filamentation within the laser emitter, is much lessdesirable, although it also can be compensated for. The nominalmultimode angular profile within the array direction beam width α isalso preferentially uniform (like curve “b”) but less uniform profilesare tolerable (curve “e” of FIG. 6 c is an example).

The construction of the organic laser arrays 300 with the generalizedlaser emitters 328 being nominally long and narrow, and preferentiallysingle mode in one dimension and multimode in the other, is motivated bythe construction of the imaging system 400, as represented by FIG. 5,which employs a linear spatial light modulator array 460, and whichprovides a pixelated line of light to a target plane 475, in a mannerthat is particularly useful for image printing and image projectionsystems. The typical spatial light modulator array 460, comprises a lineof electrically addressed pixels 463 (or modulator sites), where eachpixel has a pre-determined array direction width and cross array height.For example, each pixel 463 might have a 40 μm width and 40 μm height.Preferentially, the modulator array is constructed with a high opticalfill factor (0.9 or better), so that any gaps between adjacent pixelsare minimal. Thus, for example, a linear modulator array with a singlerow of 2048 pixels would have an active area ˜8.192 cm long, but only 40μm wide.

For maximum light efficiency, the light illuminating the linear spatiallight modulator array would match these dimensions, with minimaloverfill (some overfill of the modulator by the illuminated area mightbe tolerated to assist the system alignment). Preferentially as well,the illumination light profile in the array direction (the longdimension of the modulator array) is uniform within a few percent. Whileelectronic pattern correction can compensate for illumination patternnon-uniformity with offset or gain signals addressed to the individualpixels 463 of the modulator array 460, such corrections come at the costof pixel luminance, contrast, or modulation bit depth. Thus, the imagingsystem 400 of FIG. 5 shows the array direction light emitted by theorganic laser array 300 being optimized with a fly's eye integrator 440to provide proper illumination of the modulator array 460. As will bediscussed later, the pump light provided by the light source 360 canalso be optimized, by means of an optical pumping illumination system500, to provide proper illumination of the organic laser array 300 andthus potentially, of the modulator array 460. The system of FIG. 5 alsoprovides a cross array lenslet array 450, as well as cross array lenses455 a and 455 b, to control the cross array illumination to themodulator array 460 from the organic laser array 300. These cross arrayoptics are designed to nominally fill the narrow direction of themodulator array 460, but otherwise the actual configuration depends onthe properties of both the organic laser array 300 and the modulatorarray 460.

Generally it is preferable to illuminate the full length of the spatiallight modulator array 460 in the array direction with light from everylaser emitter in a row, rather than mapping the light from an emitter toa given portion of the modulator array. The illumination then has builtin redundancy against the failure of one or more emitters. This howevermeans that the laser emitters within a row (such as 330 a, 330 b, . . ., 330 k) should be mutually incoherent in the array (X) direction, sothat they can be overlapped without introducing significant interferencefringes in the light profile at the modulator array. If then each of thelaser emitters provides light of a uniform (or nearly so) profile (curve“b” of FIG. 6 b), the light can be directed onto the modulator arraywithout the benefit of homogenization optics. Alternately, if theemitted light profiles are non-uniform, but with random pattern ofemitter light non-uniformity from one emitter to the next across the rowof emitters, then the light from the emitters can potentially beoverlapped to provide uniform illumination by averaging without thebenefit of homogenization optics. If however, the emitter light profileshave pattern non-uniformity, such as a general fall-off at the emitteredges (such as curve “c” of FIG. 6 b), then the fall-off will bereplicated, although averaged, if the emitters are overlapped withoutthe use of homogenization optics. If the fall-off exceeds the tolerancefor the application, the problem can be corrected by over-illuminatingthe modulator array or by the use of light homogenization optics (suchas a fly's eye integrator or an integrating bar). As such lighthomogenization optics intermingle the light from a given emitter withitself, it is necessary that the emitted laser light from that emitterbe multi-mode and sufficiently incoherent (or partially coherent) thatoverlapping can occur without again introducing significant interferencefringes in the resulting illumination. On the other hand, some lightcoherence may be minimally required to obtain effective light modulation(for example, in the case of a diffractive modulator such as the GLVthat uses Schlieren optics to do filtering in a Fourier plane). As aresult, organic laser array 300 preferentially comprises at least onerow of laser emitters, where the emitters are individually multimode andalso phase de-coupled in the array (X) direction across the multitude ofemitters. As will be discussed later, the creation of area laser arraysmeans that other combinations of phase de-coupling or incoherencebetween emitters can be used.

As stated previously, in the cross array (Y) direction, it is generallypreferable that laser emitters be narrow, so that the light can becoupled efficiently into the narrow line of pixels comprising thespatial light modulator array. Although the laser emitters can bemulti-mode in the cross array direction, single mode Gaussian emissionis generally preferred, as coherent Gaussian beams propagate moretightly than does incoherent light, which further assists light crossarray light coupling into the modulator array. As before, it may bedesirable that the laser emitters be phase de-coupled from one laseremitter to the next, to avoid any cross array direction interferenceeffects, when light from multiple emitters is overlapped. Although lighthomogenization optics, such as a fly's eye integrator can be used touniformize the cross array light, a light profile that falls offgradually (such as a Gaussian beam) can be beneficial for someapplications. For example, in some printing applications, the toleranceson line placement, as related to printing artifacts such as contouring,are eased if the cross array light profile falls off gradually ratherthan abruptly. In the case of an imaging system 400 constructed with a2D organic laser array 300, it may be preferable that the beams emittedfrom the multitude of emitters from the many rows 330, 332, 334, etc.,be overlapped in the cross array direction at the modulator array as amultitude of superimposed non-interfering Gaussian beams.

Alternatively, for some linear spatial light modulator arrays, such asthe grating light valve (GLV) or the conformal grating modulator, anearly diffraction-limited laser beam is preferred in the scandirection. The present invention can accomplish this by phase-lockingthe emitters in the cross array (Y) direction. This is accomplished byreducing the pitch p2 in the narrow direction such that the circulatinglaser modes within neighboring emitters interact with each other andbecome coherently coupled. The phase-locked emitters will then emitlight coherently in the cross array direction in a so-called “supermode.” The super modes are identical to the transverse modes that areproduced by conventional laser systems, and are well-known to thoseskilled in the art. The fundamental mode is a Gaussiandiffraction-limited beam (in the cross-array direction) that can befocused on the spatial light modulator array without the necessity ofoverlapping the individual emitters. It should be noted that in phaselocked laser arrays, higher order super modes, other than thefundamental Gaussian mode, are often dominant. These higher order supermodes or multiple super modes can also be focused onto the spatial lightmodulator array, although interference fringes as described above aregenerally produced with multiple super modes. However, in many scanningapplications, these are not visible in the final image because thescanning action washes out the interference fringes with fine pitch.

One advantage of phase-locking the emitters in the cross array (Y)direction is that it provides a much higher fill factor for laseremission, thereby yielding higher light output per unit area from theorganic laser array 300. However, in practice the total area over whichthe laser emitters can be phase locked is limited by a variety ofeffects, including thermal gradients, material uniformity and pumpuniformity. The two-dimensional organic laser array 300 in FIG. 4 eshows an alternate embodiment with groups of phase-locked emitters 305providing a high fill factor with high total light output. In effect,each emitter of organic laser array 300 is replaced by a group ofphase-locked emitters 305. Advantageously, for the purposes of theapplications and systems described in this application, organic laserarray 300 could be constructed with a given group of phase-lockedemitters 305, providing a laser super mode, having different lightemission properties than a nearby or adjacent second group of phaselocked emitters 305. For example, one group of phase locked emitters 305could provide a super mode at one nominal laser wavelength (540 nm forexample), while another group of phase locked emitters 305 provides asuper mode at another nominal laser wavelength, which could be in thesame color band (550 nm for example) or in another color band (625 nmfor example).

The organic laser array 300 depicted in FIG. 4 a is illuminatedsimplistically by a light source 360 that provides optical pump light tothe laser array. Also, by means of electrical leads 370, FIG. 4 aprovides the alternative that organic laser array 300 could beelectrically pumped rather than optically pumped, such that inputelectrical energy excites the organic gain media into a light emission,with the cavity structure then supporting lasing. However, as previouslynoted, for various reasons it is preferable to utilize optical pumpingwith organic laser arrays, such that light λi from the pump sourceexcites the gain media into high light emitting energy states. There ishowever much more that can be done to optimize the illumination of theorganic laser array 300 by light source 360, as well as the beam shapingof the emitted laser light λc that is directed onto the spatial lightmodulator array 460, and the design of the organic laser array 300, soas to fulfill the intention to provide an optimized imaging system 400.Towards that end, FIGS. 7 a through 7 h illustrate variousconfigurations for modulation optical systems 410 that can be utilizedadvantageously to build imaging systems employing organic laser arrays300.

As compared to the imaging system 400 depicted in FIG. 5, FIG. 7 aillustrates a cross sectional YZ plane view of a modulation opticalsystem 410, showing the cross array direction illumination of spatiallight modulator array 460. Thus, a single laser emitter (330 a forexample) from each row of laser emitters 330, 332, 334, etc., of theorganic laser array 300 is depicted. The individual laser emitters eachemit light, which is formed into a nominally collimated beam by alenslet of combiner lenslet array 433. Combiner field lens 430 causeseach of the collimated beams to be refocused at the spatial lightmodulator array 460, such that magnified images of each laser emitterare provided, which are overlapped onto each other, filling the narrowwidth (40 μM for example) of the modulator array. Although FIG. 7 a doesshow an electrical lead 370 through which electrical pumping the organiclaser array 300 could originate, greater detail is provided of anoptical pumping illumination system 500 for the organic laser array 300,which includes a lamp 505, an illumination relay lens 530, and anillumination field lens 535.

In this configuration, lamp 505, which comprises electrodes 510 and areflector 507 of elliptical profile, is generally an arc lamp. Forexample the lamp could be a high pressure xenon short arc lamp or a highpressure mercury short arc lamp, mounted in a surface of rotationreflector 507. Optical filter 520 eliminates source light outside thedesired UV pump light spectral band. Another optical filter, leakysource filter 525, could be included in this system, after the organiclaser array 300, to remove any residual pump light that has leakedthrough the laser array. The amount of leakage light will depend on boththe optical conversion efficiency and the fill factor of the laseremitters 328 on the active area of the substrate 310 (per FIG. 4 b).Although xenon sources could be used for optical pumping with UV and lowblue spectrum light, as xenon lamps mostly emit visible and IR light,the optical efficiency would be very low. The emitted light, which isroughly focused by the elliptical reflector, is then collected by thecondensing optics, comprising illumination relay lens 530 and anillumination field lens 535. These lenses nominally cause the organiclaser array to be flood illuminated by telecentrically incident light.

In the prior discussions, the general properties of the organic laserarray 300 of the present invention, as relates to the structure and beamproperties of the individual laser emitters, and the entire laser array,have been discussed, as has the general combination of the laser arraywith an optical pumping illumination system (see FIG. 7 a). But it hasnot yet been fully described how the two can be combined to provide aunique and advantaged imaging system. As one example, with FIG. 4 a as areference, an organic laser array 300 could be constructed where tworows of laser emitters, such as 330 and 332 for example, are designed toemit red light at a nominal wavelength of 630 nm. Likewise, the two rowsof laser emitters 334 and 336 could emit green light at a nominalwavelength of 540 nm, while the two rows of laser emitters 338 and 340could emit blue light at a nominal wavelength of 460 nm. Thus, theincoherent light emitted by a light source, which in the case of FIG. 7a is lamp 505, pumps an organic laser array 300, whose emitters thencollectively provide laser light at various wavelengths in the visiblespectrum. This laser light can then be optically combined to form a lineof white laser light incident on spatial light modulator array 460. Asthe individual pixels 463 of spatial light modulator array 460 areaddressed with control signals, and the spatial light modulator array460 is imaged to a target plane by an imaging lens 470, a modulated lineof white laser light can provided at a target plane. If the systemfurther included a scanner (such as a galvo or polygon (not shown inFIG. 7 a)), this line of modulated white laser light could be scanned toprovide an addressed two dimensional image. Such a system could be used,for example, for high brightness, limited view angle signage, oralternately for color image printing or projection, provided that thecolor beams from the organic laser array 300 were changing in a colorsequential manner. Systems can also be configured with three organiclaser arrays 300, one per color, for use in higher power image printingor image projection applications, where each color modulated signal mustbe provided continuously. The various designs and applications for theorganic laser array 300 will be better explained, after some of thevarious configurations for illuminating the organic laser array 300 arefurther explored.

In the system as illustrated in FIG. 7 a, the illumination of theorganic laser array 300 is likely not uniform within a few percent. Forexample the electrodes 510 typically introduce shadows in the center ofthe beam that could lower the on axis intensity at the laser array.Alternately if the arc is imaged to the laser array, the resultingillumination typically will gradually fall-off in a Gaussian likemanner. If the optical pumping illumination system of FIG. 7 a wasconfigured as a traditional Koehler style system, sufficient uniformitymight be provided for an application where the cross array illuminationtolerance at the laser array is relaxed.

The system of FIG. 7 b illustrates an alternate optical pumpingillumination system 500 within a modulation optical system 410, as seenwith a cross sectional XZ view. In this case, laser emitters 330 a, 330b, 330 c, etc. from only a single row of laser emitters 330 are visiblein the illustration. As previously discussed, it is generally desirablein this plane to illuminate the linear spatial light modulator array 460with uniform light. For this discussion it is assumed that the quantumconversion efficiency of pump light into lasing light is highly uniformacross the organic laser array, such that uniform illumination of thelaser array translates into uniform power emitted from laser emitter tolaser emitter across the array. In that case, the uniformity of theillumination to the laser array principally determines the uniformity ofillumination to the modulator array. The optical pumping illuminationsystem of FIG. 7 b then includes both a lamp 505 and lighthomogenization optics, which in this case is a fly's eye integrator 440.As is well understood in the art, a fly's eye integrator breaks an inputlight beam into a number of smaller beamlets, and then overlap imagesthem to create uniform illumination. In the case of the system of FIG. 7b, the fly's eye integrator could comprise cylindrical optics, withoptical power only in the XZ plane, so that only the array directionillumination of the organic laser array is homogenized. Alternately, ifit is also important to homogenize the cross array directionillumination for light uniformity within a few percent, then the fly'seye integrator 440 could utilize spherical optics, and thus providelight homogenization along both meridians. A field lens (not shown)could be placed prior to linear spatial light modulator array 460, toeither make the illumination telecentric to the modulator array, oralternately, to enhance light coupling through the imaging lens 470, byimaging light into the pupil of that lens.

To further exemplify alternatives for optical pumping of the organiclaser array 300, FIG. 7 b depicts modulation optical system 410 with alamp 505, where the electrodes 510 are viewed in cross section from theend. This is generally illustrative of the use of a medium pressuremercury lamp light source, which has two end electrodes bridged by along arc, from which light is emitted. As another alternative, anexcimer lamp that generates light in the gap between two parallel longelectrodes, could be used. Both the medium pressure mercury lamp and theexcimer lamp are more efficient UV light sources than is a xenon lamp.Light collection from such lamps can be efficiently achieved usingcylindrical reflectors, rather than the surface of rotation reflectordiscussed with FIG. 7 a. In the case of FIG. 7 b, lamp 505 utilizes areflector 507 which is a cylindrical elliptical, with the reflectorhaving optical power to focus light only in the cross array direction(XZ plane). Alternately, the system of FIG. 7 b could be used with suchan elongate UV light source while using a cylindrical ellipticalreflector having optical power in the array direction, or with acylindrical parabolic reflector, or with other reflector profiles. Ofcourse, the system of FIG. 7 b could be constructed with a short arclamp and a surface of rotation reflector as in FIG. 7 a.

The system of FIG. 7 c illustrates another alternate optical pumpingillumination system 500 within a modulation optical system 410, as seenwith a cross sectional YZ view, in which a lamp 505 with a reflector 507with a parabolic profile illuminates the organic laser array 300 with“collimated” light. The cross-sectional view shows multiple rows oflaser emitters 330, 332, 334, etc., as represented by single laseremitters (330 a for example) for the organic laser array 300. As withthe system depicted in FIG. 7 a, the electrodes block light, therebycreating a shadow (low intensity region) in the center of the beam thatwill only be partially filled in as the illumination light beampropagates. Again, light uniformizing optics, such as the fly's eyeintegrator depicted in FIG. 7 b, can be used to improve the illuminationof the laser array, in the cross array direction (YZ), the arraydirection (XZ), or both. Alternately, a diffuser 515, such as aholographic diffuser from Physical Optics Inc. of Torrance, Calif.,could be used to improve illumination uniformity to the laser array.

The system of FIG. 7 c is also depicted as operating without the benefitof combiner lenslet array 433. The primary function of combiner lensletarray 433 is to collect/collimate the light emitted by organic laserarray 300 with mutually incoherent emitters so that brightness isconserved and LaGrange is limited. In optical systems, the term LaGrange(or etendue) refers to a quantity, which is the product of the spatialextent (H) of the source and the angular extent (θ) of the source. Inthe case of the organic laser array, the array direction LaGrange for asingle emitter is E=H*θ=(L/2)*α, while the cross array directionLaGrange for a single emitter is E=H*θ=(w/2)*β, where the dimensionalquantities are defined in FIGS. 4 a and 4 b. In the case of FIG. 4 a,the combiner lenslet array 433 nominally collimates the laser light fromeach laser emitter in the cross array direction. To first order, thishas the effect of limiting the cross array LaGrange to being the productof the number (N) of rows of laser emitters and the cross arraydirection LaGrange of an emitter in a row, or E=N* (w/2)*β. Likewise, inthe case of FIG. 7 b, the combiner lenslet array 433 limits the LaGrangecollected from the organic laser array 300 to being the product of thenumber (M) of laser emitters in a row and the array direction LaGrangeof an emitter in a row, or E=M*(L/2)*α. In contrast, in the system ofFIG. 7 c, the light from organic laser array 300 is collected withoutthe benefit of a combiner lenslet array 433, and the effective crossarray LaGrange is E=(Wa/2)*β, which is calculated including with thefull array width Wa, and thus including the spaces between the rows ofemitters. As a result, the cross array LaGrange ((Wa/2)*β) collected forthe case of FIG. 7 c is much larger than the cross array LaGrange(N*(w/2)*β) collected for the case of FIG. 7 a. Thus brightness, whichis the ratio of the collected power over the emitting extent (LaGrange),is much larger for the case of FIG. 7 a than it is for the case of FIG.7 c (assuming that the organic laser arrays 300 of FIGS. 7 a and 7 cemit the same total power and also that the combiner lenslet array 433introduces only modest light losses from absorption or scattering). Thisin turn means that the brightness at the spatial light modulator array460 is higher, as it then would be at a target plane. The increasedbrightness translates into the ability to provide a higher power densityor a reduced angular extent, either of which may improve the operationof the overall system. Although the combiner lenslet arrays 433discussed in relation to FIGS. 7 a and 7 b were implied to havecylindrical construction (optical power in one axis only), combinedlenslet array 433 can comprise spherical lens elements, so that thecollected LaGrange is minimized in both planes. Also, it should be notedthat the calculation of LaGrange across the organic laser array 300 wassomewhat simplified. For example, in the cross array direction, theLaGrange of a single mode laser emitter providing a Gaussian beam can becalculated as E=λ/π, which introduces a wavelength dependence. Thismeans that in organic laser arrays 300 comprising laser emitters withsubstantially variant wavelengths (such as red (630 nm) and green (540nm)), the total LaGrange for the array is not a simple product of theemitter LaGrange and the number of emitters.

The previous discussion has assumed that the emitters in the scandirection are mutually incoherent (i.e. not phased-locked). In thephase-locked case, the LaGrange is dictated by the nature of thesuper-modes produced by the phase-locked array. For the special case ofthe fundamental super-mode, the LaGrange is the diffraction-limitedGaussian beam, E=λ/π. Thus, beam combining is not useful in the scandirection when the organic laser array 300 is phase-locked in the scandirection.

In most systems, the design criteria for the cross array direction willbe determined by the optical power requirements and the cross arrayLaGrange limitations of the modulator array, although constraints at thetarget plane may also apply. If the allowed cross array LaGrange isquite large (large pixel width and large NA), it may be sufficient tooverlap cross array incoherent Gaussian or small mode beams without theuse of a cross array combiner lenslet array 430 (as in FIG. 7 c). If thecross array LaGrange is somewhat smaller, it may be sufficient tooverlap cross array incoherent Gaussian beams while using a combinerlenslet array 430 to optically remove the spaces between the rows ofemitters (as in FIG. 7 a). If the allowed cross array LaGrange is verysmall, it may be necessary to have the laser emitters phase lockedacross the entire laser array to produce a cross array super-mode, orphase locked in the manner of FIG. 4 e, with groups of phase lockedemitters 305.

The system of FIG. 7 d depicts an alternate optical pumping illuminationsystem 500 where the pump light source is an LED array 550 used toilluminate the organic laser array 300. In this case, the LED array 550can either be an inorganic solid state device, or an organic or polymerdevice (O-LED or P-LED), provided that the emitted light covers the UVto low-Blue pump spectrum needed for visible organic lasers. The LEDarray 550 consists of a series of LED emitters 553, which typically emithighly divergent light. In the system of FIG. 7 d, which is shown as aYZ cross sectional view, the light from the LED emitters 553 iscollected and re-imaged in overlapping fashion at the organic laserarray 300 by illumination lenslet array 540 and illumination combinerlens 537. Illumination field lens 535 is utilized to make theillumination nominally telecentric to the organic laser array 300. As inprevious cases, overlap flood illumination of the organic laser array300 by the light from the LED emitters 553 will provide redundancyagainst the failure of individual emitters, but not necessarilyillumination uniformity. However, again, in the YZ plane, whichcorresponds to the cross array direction at the modulator array 460,generally redundancy is required while non-uniformity can be tolerated.But, if each of the LED emitters 553 emit generally uniform light, thenthe light from the multitude can be combined at the organic laser array300 to provide uniform illumination. Edge roll off effects could then besolved most simply by adding extra LED emitters at the edges of the LEDarray 550, so that the laser array is actually over-illuminated.

Alternately, uniform illumination of the organic laser array 300 can beprovided by combining the LED array 550 with a fly's eye integrator 440,as depicted in the optical pumping illumination system 500 of FIG. 7 e.The system of FIG. 7 e is shown configured with the optics of the fly'seye integrator 440 having power in the XZ plane, with the intention ofnominally providing uniform illumination in the array direction at boththe organic laser array 300 and the spatial light modulator array 460.Of course, the fly's eye integrator 440 can be used to provide uniformillumination in only the cross array direction by using cylindricaloptics with power in the YZ plane, or to provide uniform illumination inboth the array and cross array directions by using lenses and lensletswith spherical cross-sectional profiles.

As another alternative, FIG. 7 f illustrates a YZ plane cross-sectionalview of an optical pumping illumination system 500 where the LED array550 illuminates the organic laser array 300 directly, without thebenefit if an intermediate optical system. In such a system, it would bepreferable to have the light from any LED emitter 553 illuminate amultitude of laser emitters (such as 330 a, 330 b, 332 a, 332 b) in oneor two dimensions, to provide a partial pump source redundancy, althoughless so than the prior cases where each LED emitter flood illuminatesthe entire laser array. The system of FIG. 7 f has fewer components,which would provide both a lower system cost and a more compact systemas compared to the prior examples.

The exemplary optical pumping illumination systems of FIGS. 7 b and 7 eboth utilized fly's eye integrators 440 to prepare the lightilluminating the organic laser array 300 to the desired level ofuniformity. Although the fly's eye integrator can be preferred due toits design flexibility and performance, other optics, including lightdiffusers, fiber arrays, and integrating bars can be used in providinguniform illumination. FIG. 7 g illustrates an alternate configuration,where an integrating bar (also known as a light pipe) 480 is used tohelp provide uniform illumination of the laser array in the XZ plane(array direction for the spatial light modulator array 460). Condensorrelay lens 485 images the output face of the integrating bar 480 ontothe organic laser array 300, with the possible assistance of fieldlenses (not shown) to improve performance.

As yet another alternative, FIG. 7 h illustrates an optical pumpingillumination system 500 where the organic laser array 300 is illuminatedby a pump laser 570, whose output beam is modified and prepared by beamshaping optics 575. In this case, the beam shaping optics 575 aredepicted as a two lens simple beam expander, although other opticalsystems, including a single lens, prism beam expanders, telescopicexpanders such as a three lens Keplerian system, and light integratorssuch as a fly's eye system or a Gaussian to “top-hat” beam converter,could be used to prepare the laser beam from pump laser 570 toilluminate the organic laser array 300.

As yet one more alternative, FIG. 7 i illustrates an XZ planecross-sectional view of an optical pumping illumination system 500,where an LED array 550 is the pump source that illuminates the organiclaser array 300 directly, and the organic laser array 300 in turn isimaged onto the spatial light modulator array 460. As shown, this systemis simplified and fairly compact, although any cross array optics(optical power in the XZ plane) are not shown. The main advantage ofthis system is that illumination levels can be controlled to compensatefor variations in modulation performance from pixel 463 to another pixel463 across the spatial light modulator array 460. In greater detail,this system provides the illumination light from the LED array 550 tothe organic laser array 300 directly, without intervening lighthomogenization optics. Then, by controlling the addressed signals to theLED emitters 553 of the LED array 550, the illumination across theorganic laser array 300 is deliberately varied. The organic laser array300 will emits its' light, with a profile generally matched to that fromthe LED array 550. The profile is varied so that the light emitted bythe organic laser array 300, when re-imaged onto the spatial lightmodulator array 460, compensates for the variations in modulatorperformance. This system will generally work better to compensate forpattern performance variations across the spatial light modulator array460, than abrupt pixel to pixel variations. It could also be used tocorrect for vignetting and cos⁴θ fall-offs in the imaging lens 470.

In the initial discussion concerning the use of an organic laser array300, combined with optical pumping, to form a multi-color modulatedlaser light source useful for printing or projection, the potential fora color sequential system utilizing a single organic laser array 300arranged with a pattern of RGB laser emitters, was discussed. This canbe better understood in relation to the modulation optical system 410 ofFIG. 8 a. In this system, the organic laser array 300 is preceded by anillumination modulator 555, which modulates the incident illuminationlight. In the example shown in FIG. 8 a, two illumination modulatorpixels (such as 557 a and 557 d) control the pump illumination to theblue laser emitters of organic laser array 300. Likewise, othermodulator pixels control the pump illumination to the green and redemitters. The net illumination to the spatial light modulator array 460can be driven color sequentially, by turning the pixels of theillumination array ON or OFF in a color sequential manner. In such asystem, it is ideal to map the pattern of pixels on the illuminationmodulator 555 to the organic laser array 300 with little spillage, so asto minimize color crosstalk. An optical system (not shown) could beinserted if needed between the illumination modulator array 555 and theorganic laser array 300, to help minimize cross talk between addressedcolors. The illumination modulator 555 could for example be atransmissive LCD array device, used in combination with a pre-polarizingfilter 560 a and polarization analyzing filter 560 b. It is generallypreferable to locate the illumination modulator 555 prior to the organiclaser array 300, rather than after it, as the pump source illuminationcan be readily increased to compensate for transmission losses throughthe illumination modulator 555 and associated filters.

In FIG. 8 b, a second modulation optical system 410 which can providecolor sequential operation for use in image printing or image projectionis depicted, which partially comprises three modulation channels 580 a,580 b, 580 c. Each modulation channel has its own optical pumpingillumination systems 500 and organic laser array 300, from which theemitted laser light is combined by a combining prism 655 tosimultaneously illuminate spatial light modulator array 460. Forsimplicity, the optical pumping illumination system 500 depicted in FIG.8 b utilize the compact system depicted in FIG. 7 f, although any of theoptical pumping illumination systems depicted in FIGS. 7 a-7 h could beutilized. Preferably each optical pumping illumination system 500corresponds to a given color, such that for example, system 500 aprovides blue light, system 500 b provides green light, and system 500 cprovides red light. The combining prism 655 in FIG. 8 b is shown as anX-prism (reference U.S. Pat. No. 5,098,183 by Sonehara, for example),although other combiners such as a Philips prism (reference U.S. Pat.No. 3,202,039 by DeLang) or crossed plates could be used. In any case,the combiner will be a combination of one or more dichroic coatings,which re-direct (transmit or reflect) light based primarily on thewavelength of that light. Color sequential operation can be provided byoperating the LED arrays 550 in a periodic manner, switching from onecolor to the next, in synchronization with the image data being suppliedto the spatial light modulator array 460. Although this system is morecomplicated than that of FIG. 8 a, it does have the advantage ofpotentially providing more visible laser light in each of the colorbands, as each color has an entire organic laser array 300 as a lightsource. The design of the combining prism 655 can be advantaged comparedto most projection systems, because the spectral bandwidth of the laserlight can be rather narrow and precisely controlled.

It should be understood that there are other color sequential imagingsystem configurations where organic laser arrays 300 can be effectivelyused, besides those shown in FIGS. 8 a and 8 b. As an example, U.S. Pat.No. 5,410,370 by Jannsen describes a color sequential projection systemwhere a light source is split into three parallel color beams, which arethen scrolled across a single transmissive LCD, which supplies the imagedata. An organic laser array 300, similar to the one shown in FIG. 8 a,could be used as a replacement light source for the color filtered lampsource of the U.S. Pat. No. 5,410,370 system.

Color sequential systems can be advantageous for applications where thecost and size of the system are of paramount concern, but forapplications where system brightness or color rendition has higherpriority, such systems are disadvantaged. Thus, FIG. 8 c depicts animaging system 400, which is similar to that of FIG. 8 b, except thatthe color channels each comprise a modulation optical systems 410, eachof which are complete with both an optical pumping illumination system500 and a spatial light modulator array 460. After the three colorchannels are independently modulated, a combining prism 655 can be usedto redirect the three beams down a common optical path, where an imaginglens 470 can then project an overlapped image of the three modulatorarrays. Although this system utilizes three modulator arrays 460, and isthus disadvantaged by increased cost, the delivered brightness is atleast tripled, as the respective color signals are deliveredcontinuously. As an illustration of an imaging system 400, FIG. 8 c isincomplete, as image creation by the scanning of an image of the linearspatial light modulator arrays 460 across a target plane is not shown.It also should be understood that the imaging lens 470 has been shownthroughout this application as a simple single element lens, when inreality, a multi-element lens would be used. In the case of FIG. 8 c,imaging lens 470 could have field lens elements located between thecombining prism 655 and the spatial light modulator arrays 460.

As another alternative, which is shown in FIG. 8 d, a single,multi-color organic laser array 300 can be combined with a tri-linearmodulator array 465 to provide three color lines of independentlymodulated laser light. The organic laser array 300 can comprise multiplerows of laser emitters 330, 332, 334, etc., in an arrangement where somerows comprise red emitters, other rows comprise blue emitters, and yetother rows comprise green emitters. The organic laser array 300 issimilar to the laser array provided in the system of FIG. 8 b, exceptthat the optical pumping illumination system does not include aillumination modulator 555 to provide color sequential operation, butrather the pump source provides light continuously. Rather, the lightfrom the rows of laser emitters 330, etc. of a given color band (greenfor example) are condensed onto one modulator array of the tri-linearmodulator array 465, while light from the other color rows of laseremitters are condensed respectively onto the other modulator arrays. InFIG. 8 d, a combiner lenslet array 433 and a combiner field lensletarray 467 are used in combination to condense light on the tri-linearmodulator array 465. Each modulator array is supplied with image data ofthe respective color in an appropriately synchronized manner. Thetri-linear modulator array 465 can then be imaged to a target plane byan imaging lens, which is shown as two elements (field lens 470 a andimaging lens 470 b), where scanning will enable reconstruction of thefull two dimensional, three color image. The tri-linear modulator array465 can be constructed monolithically, or with three closely spacedseparate modulator arrays 460.

The imaging systems depicted in FIGS. 8 a, 8 b, and 8 c illustrateconceptual designs by which one or more organic laser arrays 300 can beused in combination with linear spatial light modulator arrays 460 tocreate a line of modulated full color laser light. FIGS. 9 a and 9 billustrate more fully the potential use of imaging systems employingorganic laser arrays in printing and projection display applications. Inparticular, FIG. 9 a depicts an imaging system applicable for printing,where the a printhead 600 comprises an imaging lens 470, which projectsan image of the linear spatial light modulator array 460 onto a lightsensitive media 620. The printhead 600, which is built on a mechanicalframe 605, is translated laterally, while the media 620 is rotated by adrum 610, so that a printed swath 625 of image data is written onto themedia 620. For simplicity, the organic laser array 300 is shown asoptically pumped by a light source 360, although some of the opticalpumping illumination systems depicted in FIGS. 7 a through 7 g could beused in the system. Alternately of course, electrically pumped organiclaser arrays could be used. To provide full color imaging with a singleprinthead, this system would require a multi-channel approach with threeorganic laser arrays 300, as in FIG. 8 c, or a system with a tri-linearmodulator array 465, as described with FIG. 8 d, or a color sequentialconfiguration with one or more organic laser arrays 300.

In prior discussions, various attributes of the organic laser arrays 300of the present invention have been described. Initially, as shown inFIGS. 4 a and 4 b, the advantageous construction of organic laser arrays300 comprising multiple rows of laser emitters that are multi-mode inthe array direction and single mode in the cross array direction wasdiscussed. The preferred beam profiles of the emitted laser light werethen discussed with relation to FIGS. 6 a-6 c. The additional point wasthen made that the emitted laser light across the organic laser array300 should be mutually incoherent (phase de-coupled) from laser emitterto laser emitter, even if the laser emitters nominally emit the samewavelength light, in order to minimize interference fringe effects whenthe light is overlapped. Advantageous constructions of the organic laserarrays 300 were subsequently discussed, where a given laser array mightprovide a constant color (all green laser light) or laser light of thethree primary colors (RGB) from a single device.

However, yet another point needs to be made, wherein the design of theorganic laser array 300 provides advantages to the design of the imagingsystem 400. In the prior examples of FIGS. 8 b, 8 c, and 9 b, the colorchannels are provided with a given organic laser array 300 providing“red”, “green” or “blue” light. Moreover, examples have been given wherethe representative wavelengths were 630 nm, 540 nm, and 460 nm, wheregenerally the bandwidth at each of these lasing wavelengths is typically1.0 nm. The advantages of the organic laser array 300, which include theability to pattern emitters, pattern devices, and select the lasingwavelength, have greater possibilities than so far described. Certainly,in many visual imaging systems, it can be advantageous to provide narrowspectral widths in each spectral band, as the color gamut expands andthe specification for the color filters and prisms ease. On theotherhand, lasers with narrow bandwidths (less than ˜3 nm, andparticularly less than ˜1 nm) can suffer speckle when this coherentlaser light interferes with itself, such as due to scatter from a roughscreen surface. Speckle is a special interference effect that candramatically reduce uniformity. In the representative optical pumpingillumination systems 500 where light homogenizers are used, such as thefly's eye integrator or an integrating bar, interference can occur whenlight from a laser emitter is split up and overlapped with itself.Interference is avoided if light from adjacent laser emitters of organiclaser array 300 is mutually incoherent, even if the laser wavelength isnominally the same. Overlap of light from the many emitters will tend towash out speckle. However, there can be a tendency for adjacent emittersof the same nominal wavelength to cluster in mutually coherent groups,with the effect in the system of amplifying laser speckle. Laser specklecan be further reduced by designing the laser array to consist of laseremitters with bandwidths of 4 nm or greater. However, for the VCSELstructure described in FIGS. 1-3, this would require the use of a verylow-finesse microcavity, which would imply a high pump threshold densitydue to the transmission loss through the mirrors. Alternately, specklecan be reduced by expanding the defining lasing wavelengths for a givencolor to consist of multiple wavelengths. For example, the green lightcould consist of laser emitters operating at multiple wavelengths, suchas 540 nm, 545 nm, and 550 nm, preferably with an approximately equalnumber of laser emitters for each wavelength. Preferably, the laserwavelengths would vary approximately uniformly throughout this 10 nmrange. Again with respect to exemplary FIGS. 8 b, 8 c, and 9 b, in agiven organic laser arrays 300, the nominal emitter wavelengths could bevary randomly or periodically from emitter to emitter, or vary inclusters across the array, or vary from row to row, etc.

It should also be pointed out that the design of the organic laserarrays 300, with control of both the nominal lasing wavelengths withinthe visible spectrum, as well as the size and number of laser emittersdevoted to a specific color spectrum (red, green, and blue respectively)provides an additional advantage for color balancing. In particular, thenumber of laser emitters 328 of each color, as well as the wavelength ofthose laser emitters, can be adjusted to provide a desired color balanceas needed for a given application. For example, in printingapplications, a larger number of blue emitters may be needed, if themedia 620 has a low blue exposure sensitivity.

Alternately, FIG. 9 b shows an imaging system 400, similar to that ofFIG. 8 c, where three modulation optical systems 410 are used to providemodulated three color visible laser light as three color channels 650 a,650 b, and 650 c, which are then combined via a combining prism 655. Inthis case, a post objective scanner is depicted, where a galvanometerscanner 660 is provided after the imaging lens 470. As the galvanometerscanner 660 is swept through its motion, the imaging light is reflectedoff the galvo mirror 665 and scanned across a target plane, to provide atwo-dimensional image. If a screen is provided at that target plane, theimaging system 400 is a projection display system, but if a lightsensitive media is provided, the imaging system 400 constitutes aprinting system. Again for simplicity, basic optical pumping with alight source 360 is shown, although some of the more complete opticalpumping illumination systems 500 from FIGS. 7 a through 7 g could beused in this system.

Thus far, the organic laser array 300, as shown on FIG. 4 a, has beendescribed as consisting of multiple rows of laser emitters 330, 332,334, etc., each comprising a series of laser emitters, such as 330 a,330 b, 330 c, etc., while various combinations of variable modestructure and lasing wavelength have been discussed as being patternedacross the entire laser array, in order to be optimized for variousapplications and system configurations. It should however be understoodthat the structure of organic laser array 300 could be varied in otheruseful ways. In particular, as shown in FIG. 4 c, the organic laser 300could consist of generalized laser emitters 328 that are “indefinite” inlength. In the prior discussion related to FIG. 4 b, the generalizedlaser emitters 328 were described as having a length (L), a width (w), apitch (p) between emitters within a row, and a pitch (p2) between rowsof laser emitters. If however, the generalized laser emitters 328 werenot configured in an array pattern in X, but were extended without anintervening gap for nearly the full length of the substrate 310, then anorganic laser array 300 as depicted in FIG. 4 c would result. Forexample, a single generalized laser emitter 328, fabricated for singlemode emission in Y and multimode emission in X could be <1-5 μm wide (w)and 20 mm in length (L). The emitted laser light could have minimalspatial coherence in the long direction, and could even experiencefilamentation, which would in turn degrade the array directionuniformity. If the emitted laser light from a single generalized laseremitter 328 illuminated a spatial light modulator array 460 directly inX, or with direct imaging without light homogenization, the modulatorarray would experience the light profile non-uniformities, which wouldbe less than ideal. If however, multiple (N) rows of laser emitters 330,332, 334, etc. of generalized laser emitters 328 with very longmultimode extents in X were used, in combination with a combiner lensletarray 433 and a combiner field lens 430 (both having optical power onlyin the YZ plane), to overlap illuminate the modulator array 460, asimplified modulation optical system 410 would result that could meetthe illumination uniformity requirements. In this simplified system, thecombiner lenslet array 433 is one-dimensional, lacking optical power inthe XZ plane. Additionally with the illumination in the array direction(X relative to the modulator array) sufficiently uniform, a fly's eyeintegrator 440 or integrating bar 480 would not be needed to correct forpump source or organic laser light profile non-uniformities. For this tobe true however, the generalized laser emitters 328 across the multiplerows 330, 332, 334 could not have any pattern errors in the X direction,such as deep laser non-uniformity occurring in the same location fromone laser emitter to the next. Then, overlap imaging of the N rows oflaser emitters would average the light profiles of the individualemitters, providing uniform illumination and removing non-uniformityeffects to a considerable extent (depending on the number N of averagedrows).

It should also be understood that although the organic laser array 300is generally depicted as comprising periodically spaced rows of laseremitters (pitch “p2”), wherein each row comprises periodically a seriesof periodically spaced (pitch “p”) laser emitters, that the position ofboth the rows of laser emitters and the laser emitters within the rowscould be varied randomly, quasi-randomly, or with variable periodicity.For example, FIG. 4 d illustrates a portion of an alternate exemplaryorganic laser array 300, where the laser emitters 328 are patterned witha pitch “p” or a starting position in a given row, that vary from onerow of laser emitters to the next row. In this case, when the light fromthe (N) multiple rows of laser emitters is combined and overlapped toflood illuminate a target plane (where the modulator array 460 resides),the resulting illumination could be sufficiently uniform without the useof homogenization optics such as a fly's eye integrator. The laseremitter length (L) could also be variable within the rows of laseremitters. Likewise, as another example of an organic laser array 300construction, the nominal wavelength of laser emission could bevariable, either randomly or aperiodically for the laser emitters formedwithin the rows or laser emitters of from one row of laser emitters toanother row.

For simplicity, the various system illustrations have all depicted thelinear spatial light modulator array 460 as a transmissive device. Forexample, the modulator array 460 could be a transmissive liquid crystaldisplay (LCD). While LCDs are commonplace, the typical devices are areaarray modulators, and linear array modulators are virtually unheard of.Moreover, most LCDs operate by changing the polarization state of theincident light. Although the organic laser arrays 300 can be designed toprovide polarized laser light, the emitted laser light otherwise isgenerally un-polarized. Polarizing the light from the organic laserarray 300, so as to pair it with an LCD, would introduce a significantlight loss, unless a polarization conversion system was also used. Insuch a case, therefore, it would be preferable to design an organiclaser array 300 so that the laser emitters 328 produce polarized laserlight. This can be accomplished through the design of the emitter shape,such that, for example asymmetry of the emitter shape can inducepolarization in the emitted light. Alternately, the spatial lightmodulator array 460 could be an asymmetric Fabry-Perot etalon modulator,which is a transmissive modulator that switches between transmissive andreflective states. U.S. Pat. No. 5,488,504 by Worchesky et al. describessuch a modulator. As another transmissive modulator alternative, therolling MEMS shutter modulator described in U.S. Pat. No. 5,233,459 byBozler, could be used, as it also switches between transmissive andreflective states.

Although a transmissive modulator array is advantageous for keeping theimaging systems 400 relatively simple, a wider range of usefulreflective modulator technologies have been developed, which can be usedfor visible wavelength light modulation. These devices are generallymade using MEMS technologies, rather than electro-optical means. Viablereflective modulator arrays that can be combined with the organic laserarrays 300 in these systems include the digital mirror device (DMD)described in U.S. Pat. No. 5,535,047 by Hornbeck, the grating lightvalve (GLV) as described in U.S. Pat. No. 5,311,360 by Bloom et al., andthe conformal grating modulator described in U.S. Pat. No. 6,307,663 byKowarz. For these reflective modulators, the various imaging systems400, such as that of FIG. 9 a, would need to be appropriately modifiedto illuminate the reflective modulator array and collect the modulatedimage light. The modulated image light would be directed into theimaging lens 470, so that the modulator array could be imaged to thetarget plane. The imaging system 400 could be folded to allow collectionof the modulated image light. Alternatively, to retain a compactmechanical design, the imaging system 400 could be modified to deflectlight out of the main optical path onto the reflective modulator arrayand to send the modulated image light back into the main optical path.For grating light valves, the optical systems are Schlieren typesystems, with spatial filters placed at or near a Fourier plane todistinguish between the modulated image light and the non-image light.The Fourier plane for spatial filtering would typically be within theimaging lens 470. For the digital mirror device and the conformalgrating modulator, non-Schlieren systems can be used, with a spatialfilter located between the modulator array and the imaging lens 470.

It should be understood that this invention, as relates to organic laserarrays, and their use in illumination systems, modulation opticalsystems, and imaging systems, is described in numerous ways, but thatare other variations and obvious changes that are not described, butwhich would fall within the scope of this invention.

As an example, there are other technologies that are being developedwhich may yield multi-spectral, even multi-color, laser arrays, whichmay have both the low cost potential and design flexibility of theorganic laser array technology. In particular, quantum dot and quantumdash laser technologies have shown the potential to produce laserdevices within a wide spectral range. Quantum dot lasers use very smallclusters of atoms imbedded in a quantum well layer and surrounded bybarrier layers in three dimensions. The fluorescence wavelength of thequantum dot emitters depends not only on the type of material used (suchas cadmium selenide), but also on the diameter of the individual dots.An individual quantum dot has an optical gain related to the injectioncurrent. However, the occurrence of stimulated emission or lasing alsorequires a sufficient local density of quantum dots interacting with thewave field. That is, the macroscopic optical gain depends on the gaincharacteristics of the multiplicity of common dots. Thus, the prior artfor quantum dot lasers typically depict structures comprising an arrayof individual quantum dots, such as shown in FIG. 2 of U.S. Pat. No.5,692,003 (Wingreen et al.) or in FIG. 3 of U.S. Pat. No. 6,816,525(Stintz et al.).

The prior art for quantum dot lasers also teaches the usage ofmonolithic multi-wavelength laser arrays, such as depicted in FIG. 19 aof U.S. Pat. No. 6,600,169 (Stintz et al.) and in FIG. 28 of U.S. Pat.No. 6,816,525. These devices provide a multitude of laser emitters,providing output lasing light that varies from emitter to emitter, suchthat discrete emission wavelengths λ₁, λ₂, λ₃ . . . λ_(n) are generated.In the case of the quantum dot lasers, each individual laser emitter inturn comprises a quantum dot or quantum dash active region, with aninternal structure of appropriately sized quantum dots or dashes,containing quantum well (core) and barrier materials of the proper type.

Certainly, quantum dot laser technology represents at least a firstpotential alternative laser technology to the organic vertical cavitylaser array, for providing laser arrays with multi-spectral lasingemission over a wide spectral bandwidth. Quantum dot lasers cancurrently be produced by expensive high vacuum methods, while individualfluorescent quantum dots can be made by low cost chemical methods. Withregard to the low cost dots, they have the potential to produce usefullaser devices; however, to date no practical ones have beendemonstrated. The organic laser devices have the advantages of being lowcost and demonstrating practical lasers devices is much farther along.Nonetheless, quantum dot lasers would likely emit more light per laseremitter than can organically-based lasers.

With respect to the present invention, organic vertical cavity laserarrays are described in which there are a plurality of laser emitters,and each laser emitter has a first lateral mode structure in a firstaxis orthogonal to the laser light direction and has a second lateralmode structure in a second axis orthogonal to both the laser lightdirection and said first axis. Exemplary devices were previouslydescribed in which the laser emitters had lateral mode structures thatwere single mode along one axis, and multi-mode along the orthogonalaxis. Exemplary multi-color devices, providing primary colored light(red, green, and blue) were also described. This concept is new, notonly to the design of organic vertical cavity laser arrays andmulti-spectral vertical cavity laser arrays, but to the design ofmulti-spectral laser arrays in general. Although the precise compositionand design of the active region that provides the optical gain may vary,the use of spatially variant lateral mode structures in multi-colorlaser arrays has ongoing value. For example, in the prior art forquantum dot lasers, consideration is given to the longitudinal lasingmode structure and its relationship to the cavity length L. Minimalconsideration is given to the lateral mode structure of such quantum dotlasers. In many of the anticipated applications for quantum dot lasers,such as in DWDM systems for telecommunications, single mode lateral beamstructures would be preferred for optical coupling into waveguides andoptical fibers. In summary, the value of multispectral (multi-color)laser arrays in electronic imaging systems (such as printing andprojection systems) with lateral mode structures that vary orthogonallyto the direction of light emission has not been anticipated in the priorart, as it has been in the present invention.

Parts List

-   10 Vertical cavity organic laser structure-   20 Substrate-   30 Bottom dielectric stack-   35 Organic laser film structure-   40 Organic active region-   50 Top dielectric stack-   60 Pump beam-   65 Pump light source-   70 Laser emission-   80 Vertical cavity organic laser structure-   100 Periodic gain regions-   103 Anti-node-   105 Node-   110 Organic spacer layers-   120 Electromagnetic field pattern-   190 Phase-locked organic laser array-   200 Lasing emitters-   210 Inter-emitter regions-   220 Etched regions-   300 Organic laser array-   305 Group of phase-locked emitters-   310 Substrate-   325 Gap-   328 Generalized laser emitter-   330 Row of laser emitters-   330 a Laser emitter-   330 b Laser emitter-   330 c Laser emitter-   330 d Laser emitter-   330 e Laser emitter-   330 f Laser emitter-   330 g Laser emitter-   330 h Laser emitter-   330 i Laser emitter-   330 j Laser emitter-   330 k Laser emitter-   332 Row of laser emitters-   334 Row of laser emitters-   336 Row of laser emitters-   338 Row of laser emitters-   340 Row of laser emitters-   342 Row of laser emitters-   350 Laser light-   360 Light source-   365 Illumination light-   370 Electrical leads-   400 Imaging system-   410 Modulation optical system-   420 Optical axis-   430 Combiner field lens-   433 Combiner lenslet array-   436 Array field lens-   440 Fly's eye integrator-   450 Cross array lenslet array-   455 a Cross array lens-   455 b Cross array lens-   460 Spatial light modulator array-   463 Pixel-   465 Tri-linear modulator array-   467 Combiner field lenslet array-   470 Imaging lens-   470 a Field lens-   470 b Imaging lens-   475 Target plane-   480 Integrating bar-   485 Condensor relay lens-   500 Optical pumping illumination system-   500 a Blue light optical pumping illumination system-   500 b Green light optical pumping illumination system-   500 c Red light optical pumping illumination system-   505 Lamp-   507 Reflector-   510 Electrode-   515 Diffuser-   520 Filter-   525 Leaky source filter-   530 Illumination relay lens-   535 Illumination field lens-   537 Illumination combiner-   540 Illumination lenslet array-   550 LED array-   553 LED emitters-   555 Illumination modulator-   557 a Modulator pixel-   557 b Modulator pixel-   560 a Pre-polarizing filter-   560 b Analyzing filter-   570 Pump laser-   575 Beam shaping optics-   580 a Modulation channel-   580 b Modulation channel-   580 c Modulation channel-   600 Printhead-   605 Mechanical frame-   610 Drum-   620 Media-   625 Printed swath-   650 a Color channel-   650 b Color channel-   650 c Color channel-   655 Combining prism-   660 Galvanometer scanner-   665 Galvo mirror

1. A multi-spectral laser light source, comprising: a) a substrate; b) aplurality of laser emitters emitting laser light in a directionorthogonal to the substrate, wherein each laser emitter within saidplurality of laser emitters has a first lateral mode structure in afirst axis orthogonal to the laser light direction and has a secondlateral mode structure in a second axis orthogonal to both the laserlight direction and said first axis, each laser emitter comprising: i) afirst mirror provided on a top surface of the substrate and reflectiveto light over a predetermined range of wavelengths; ii) an active regionon a top surface of said first mirror for producing laser light; iii) asecond mirror on a top surface of said active region and reflective tolight over a predetermined range of wavelengths; c) a pumping means thatexcites said plurality of laser emitters; and wherein said laser lightemitted by said plurality of laser emitters to provide multi-spectraloutput, wherein a first group of laser emitters emits light at nominalwavelengths in one portion of the optical spectrum, and a second groupof laser emitters emits light at nominal wavelengths in a second portionof the optical spectrum.
 2. A multi-spectral laser light sourceaccording to claim 1 wherein said laser emitters are arranged inparallel rows, said laser emitters in said rows have a periodic pattern,wherein a length of each of said laser emitters, a gap between eachadjacent pair of said laser emitters, or both are varied along a fullextent of a given row.
 3. A multi-spectral laser light source accordingto claim 1 wherein said laser emitters are arranged in parallel rows,said laser emitters in said rows have a periodic pattern, wherein alength of each of said laser emitters and a gap between each adjacentpair of said laser emitters is repeated along the full extent of a givenrow.
 4. A multi-spectral laser light source according to claim 1 whereinsaid first lateral mode structure exhibits multi-mode lasing behavior;and wherein each of said laser emitters have said second lateral modestructure that exhibits a single mode lasing behavior.
 5. Amulti-spectral laser light source according to claim 1 wherein saidlaser light emitted by said plurality of laser emitters is arranged tovary within the visible spectrum; wherein each of said laser emittersprovides laser light at a given nominal emission wavelength with anemission spectral bandwidth; and wherein said nominal emissionwavelength is variable within the visible spectrum for said plurality oflaser emitters, such that the given nominal emission wavelength for onegroup of one or more of said laser emitters is different than the givennominal emission wavelength for another group of one or more of saidlaser emitters.
 6. A multi-spectral laser light source according toclaim 5 wherein said laser light emitted by said plurality of laseremitters is arranged to vary within the visible spectrum to providemultiple color output; and wherein said plurality of laser emitters arearranged in three groups of laser emitters, the first of which emitslight at nominal wavelengths in the blue portion of the spectrum, thesecond of which emits light at nominal wavelengths in the green portionof the spectrum, and the third of which emits light at nominalwavelengths in the red portion of the spectrum.
 7. A multi-color laserarray comprising: a) a substrate; b) a plurality of laser emittersemitting laser light in a direction orthogonal to the substrate, whereineach laser emitter within said plurality of laser emitters, has a firstlateral mode structure in a first axis orthogonal to the laser lightdirection and has a second lateral mode structure in a second axisorthogonal to both the laser light direction and said first axis, eachlaser emitter comprising: i) a first mirror provided on a top surface ofthe substrate and reflective to light over a predetermined range ofwavelengths; ii) an active region on a top surface of said first mirrorfor producing laser light; iii) a second mirror on a top surface of saidactive region and reflective to light over a predetermined range ofwavelengths; c) a pumping means that excites said plurality of laseremitters; d) an arrangement of said laser emitters such that saidplurality of laser emitters to form an array, comprising one or moreparallel rows of laser emitters, wherein, within a row of laseremitters, a series of said laser emitters are arranged in sequence toform a line of laser emitters that are an array direction; wherein saidparallel rows of laser emitters are arranged in a sequence along a crossarray direction; and wherein said laser light emitted by said pluralityof laser emitters is arranged to vary within the visible spectrum toprovide multi-color output, such that a group of laser emitters emitslight at nominal wavelengths in one portion of the visible spectrum, anda second group of laser emitters emits light at nominal wavelengths in asecond portion of the visible spectrum.
 8. A multi-color laser arrayaccording to claim 7 wherein each of said laser emitters within saidplurality of laser emitters has a first lateral mode structure, along afirst axis that is aligned with said array direction, that exhibitsmulti-mode lasing behavior, and wherein each of said laser emitterswithin said plurality of laser emitters has a second lateral modestructure, along a second axis that is aligned with said cross arraydirection, that exhibits a single mode lasing behavior.
 9. A multi-colorlaser array according to claim 8 wherein within each of said parallelrows of laser emitters, said laser emitters are arranged in a sequencehaving a periodic pattern, wherein the length of each of said laseremitters and the gap between each adjacent pair of said laser emittersis repeated along the full extent of a given row.
 10. A multi-colorlaser array according to claim 9 wherein said periodic pattern is thesame for all of said parallel rows of laser emitters.
 11. A multi-colorlaser array according to claim 7 wherein said laser emitters provideslaser light emitted in different portions of the visible spectrum, suchthat said plurality of laser emitters are arranged in three groups oflaser emitters, the first of which emits light at nominal wavelengths inthe blue portion of the spectrum, the second of which emits light atnominal wavelengths in the green portion of the spectrum, and the thirdof which emits light at nominal wavelengths in the red portion of thespectrum.
 12. A multi-color laser array according to claim 11 whereinsaid laser emitters emit laser light at multiple nominal wavelengthswithin a given color spectrum selected from red, green or blue spectrum.13. A multi-color laser array comprising: a) a substrate; b) a pluralityof laser emitters emitting laser light in a direction orthogonal to thesubstrate, wherein each laser emitter within said plurality of laseremitters, has a first lateral mode structure in a first axis orthogonalto the laser light direction that corresponds to multi-mode lasingbehavior and has a second lateral mode structure in a second axisorthogonal to both the laser light direction and said first axis thatcorresponds to single mode lasing behavior, each laser emittercomprising: i) a first mirror provided on a top surface of the substrateand reflective to light over a predetermined range of wavelengths; ii)an active region on a top surface of said first mirror for producinglaser light; iii) a second mirror on a top surface of said active regionand reflective to light over a predetermined range of wavelengths; c) apumping means that excites said plurality of laser emitters; d) anarrangement of said laser emitters within said plurality of laseremitters to form an array, comprising one or more parallel rows of laseremitters, wherein, within a row of laser emitters, a series of saidlaser emitters are arranged in sequence to form a line of laser emittersthat are an array direction; wherein said parallel rows of laseremitters are arranged in a sequence that is a cross array direction; andwherein said laser light emitted by said plurality of laser emitters isarranged to vary within the visible spectrum to provide multi-coloroutput, such that a group of laser emitters emits light at nominalwavelengths in one portion of the visible spectrum, and a second groupof laser emitters emits light at nominal wavelengths in a second portionof the visible spectrum.
 14. A multi-color laser array comprising: a) asubstrate; b) a plurality of laser emitters emitting laser light in adirection orthogonal to the substrate, wherein each laser emitter withinsaid plurality of laser emitters, has a first lateral mode structure ina first axis orthogonal to the laser light direction that corresponds tomulti-mode lasing behavior and has a second lateral mode structure in asecond axis orthogonal to both the laser light direction and said firstaxis that corresponds to multi-mode lasing behavior, wherein there aremany fewer modes in the second axis direction than in the first axisdirection, each laser emitter comprising: i) a first mirror provided ona top surface of the substrate and reflective to light over apredetermined range of wavelengths; ii) an active region on a topsurface of said first mirror for producing laser light; iii) a secondmirror on a top surface of said active region and reflective to lightover a predetermined range of wavelengths; c) a pumping means thatexcites said plurality of laser emitters; d) an arrangement of saidlaser emitters within said plurality of laser emitters to form an array,comprising one or more parallel rows of laser emitters, wherein, withina row of laser emitters, a series of said laser emitters are arranged insequence to form a line of laser emitters that are an array direction;wherein said parallel rows of laser emitters are arranged in a sequencethat is a cross array direction; and wherein said laser light emitted bysaid plurality of laser emitters is arranged to vary within the visiblespectrum to provide multi-color output, such that a group of laseremitters emits light at nominal wavelengths in one portion of thevisible spectrum, and a second group of laser emitters emits light atnominal wavelengths in a second portion of the visible spectrum.
 15. Amulti-color laser array according to claim 14 wherein said emitters emitlight at nominal wavelengths that is in one of the primary colors.
 16. Amodulation optical system with a multi-spectral laser array comprising:a) a multi-spectral laser array comprising: i) a substrate; ii) aplurality of laser emitters emitting laser light in a directionorthogonal to the substrate, wherein each laser emitter within saidplurality of laser emitters has a first lateral mode structure in afirst axis orthogonal to the laser light direction and has a secondlateral mode structure in a second axis orthogonal to both the laserlight direction and said first axis, each laser emitter comprising: a1)a first mirror provided atop the substrate and reflective to light overa predetermined range of wavelengths; a2) an active region for producinglaser light; a3) a second mirror provided above the active region andreflective to light over a predetermined range of wavelengths; a4) anarrangement of said laser emitters within said plurality of laseremitters to form an array, comprising one or more parallel rows of laseremitters, wherein, within a row of laser emitters, a series of saidlaser emitters are arranged in sequence to form a line of laser emittersin an array direction; a5) a pumping means that excites said pluralityof laser emitters; wherein said parallel rows of laser emitters arearranged in a sequence in a cross array direction; wherein said laserlight emitted by said plurality of laser emitters is arranged to varywithin the optical spectrum to provide multi-spectral output, such thata group of laser emitters emits light at nominal wavelengths in oneportion of the optical spectrum, and a second group of laser emittersemits light at nominal wavelengths in a second portion of the opticalspectrum; b) optical means, comprising laser beam shaping optics forpreparing laser light from said multi-spectral laser array to illuminatea spatial light modulator array; and c) wherein said spatial lightmodulator array comprises an arrangement of individually addressedmodulator pixels, each of which alter incident laser light in accordancewith applied drive signals specific to each of said pixels.
 17. Amodulation optical system according to claim 16 wherein said firstlateral mode structure is multi-mode and said second lateral modestructure is single mode.
 18. A modulation optical system according toclaim 16 wherein said laser array is multimode in both directions, withmany fewer modes in the second axis direction than in the first axisdirection.
 19. A modulation optical system according to claim 16 whereinsaid laser array is single mode in the second axis direction, andmulti-mode in the first axis direction, and the emitters extend nearlythe full length of the array in the first axis direction.
 20. Anelectronic imaging system with a multi-spectral laser array comprising:a) one or more multi-spectral laser arrays, each comprising: i) asubstrate; ii) a plurality of laser emitters emitting laser light in adirection orthogonal to the substrate, wherein each laser emitter withinsaid plurality of laser emitters, has a first lateral mode structure ina first axis orthogonal to the laser light direction and has a secondlateral mode structure in a second axis orthogonal to both the laserlight direction and said first axis, each laser emitter comprising: a1)a first mirror provided on atop the substrate and reflective to lightover a predetermined range of wavelengths; a2) an active region forproducing laser light; a3) a second mirror provided above the activeregion and reflective to light over a predetermined range ofwavelengths; a4) an arrangement of said laser emitters within saidplurality of laser emitters to form an array, comprising one or moreparallel rows of laser emitters, wherein, within a row of laseremitters, a series of said laser emitters are arranged in sequence toform a line of laser emitters in an array direction; a5) a pumping meansthat excites said plurality of laser emitters; wherein said parallelrows of laser emitters are arranged in a sequence in a cross arraydirection; wherein said laser light emitted by said plurality of laseremitters is arranged to vary within the optical spectrum to providemulti-spectral output, such that a group of laser emitters emits lightat nominal wavelengths in one portion of the optical spectrum, and asecond group of laser emitters emits light at nominal wavelengths in asecond portion of the optical spectrum; b) optical means, comprisinglaser beam shaping optics for preparing laser light to illuminate aspatial light modulator array; which comprises modulator pixels that areindividually addressed with applied drive signals bearing data; and c)imaging optics to re-image said spatial light modulator array onto atarget plane.
 21. An electronic imaging system according to claim 20wherein said electronic imaging system is a printing system with a lightsensitive media located at the target plane.
 22. An electronic imagingsystem according to claim 20 wherein said first lateral mode structureis multi-mode and said second lateral mode structure is single mode. 23.An electronic imaging system according to claim 20 wherein saidmulti-spectral laser arrays provide light over a predetermined range ofwavelengths comprising one or more of the primary colors.